wdiff draft-ietf-gnap-core-protocol-02.txt draft-ietf-gnap-core-protocol-03.txt

GNAP J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track A. Parecki
Expires: 21 May 10 July 2021 Okta
F. Imbault
acert.io
17 November 2020
6 January 2021

Grant Negotiation and Authorization Protocol
draft-ietf-gnap-core-protocol-02
draft-ietf-gnap-core-protocol-03

Abstract

This document

GNAP defines a mechanism for delegating authorization to a piece of
software, and conveying that delegation to the software. This
delegation can include access to a set of APIs as well as information
passed directly to the software.

This document has been prepared by the GNAP working group design team
of Kathleen Moriarty, Fabien Imbault, Dick Hardt, Mike Jones, and
Justin Richer. This document is intended as a starting point for the
working group and includes decision points for discussion and
agreement. Many of the features in this proposed protocol can be
accomplished in a number of ways. Where possible, the editor has
included notes and discussion from the design team regarding the
options as understood.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on 21 May 10 July 2021.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 4
1.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Elements . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Sequences . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4.1. Redirect-based Interaction . . . . . . . . . . . . . 10
1.4.2. User-code Interaction . . . . . . . . . . . . . . . . 12
1.4.3. Asynchronous Authorization . . . . . . . . . . . . . 14 15
1.4.4. Software-only Authorization . . . . . . . . . . . . . 15 16
1.4.5. Refreshing an Expired Access Token . . . . . . . . . 16 17
2. Requesting Access . . . . . . . . . . . . . . . . . . . . . . 17 18
2.1. Requesting Resources . . . . . . . . . . . . . . . . . . 19 20
2.1.1. Requesting a Single Access Token . . . . . . . . . . 19 20
2.1.2. Requesting Resources By Reference . . . . . . . . . . 21 24
2.1.3. Requesting Multiple Access Tokens . . . . . . . . . . 23 26
2.1.4. Signaling Token Behavior . . . . . . . . . . . . . . 25 28
2.2. Requesting User Information . . . . . . . . . . . . . . . 26 29
2.3. Identifying the RC . . . . . . Client Instance . . . . . . . . . . . . . 27 30
2.3.1. Identifying the RC Client Instance . . . . . . . . . . . . . 29 32
2.3.2. Identifying the RC Client Instance Key . . . . . . . . . . . . . . . 30 33
2.3.3. Providing Displayable RC Client Instance Information . . . . . . . . 31 34
2.3.4. Authenticating the RC . . . . . . . Client Instance . . . . . . . . . 31 34
2.4. Identifying the User . . . . . . . . . . . . . . . . . . 32 35
2.4.1. Identifying the User by Reference . . . . . . . . . . 33 36
2.5. Interacting with the User . . . . . . . . . . . . . . . . 33 36
2.5.1. Redirect to an Arbitrary URL . . . . . . . . . . . . 35 38
2.5.2. Open an Application-specific URL . . . . . . . . . . 36 38
2.5.3. Receive a Callback After Interaction . . . . . . . . 36 39
2.5.4. Display a Short User Code . . . . . . . . . . . . . . 38 41
2.5.5. Indicate Desired Interaction Locales . . . . . . . . 38 41
2.5.6. Extending Interaction Modes . . . . . . . . . . . . . 39 41
2.6. Declaring RC Client Capabilities . . . . . . . . . . . . . . . . 39 42
2.7. Referencing an Existing Grant Request . . . . . . . . . . 39 42
2.8. Requesting OpenID Connect Claims . . . . . . . . . . . . 39
2.9. Extending The Grant Request . . . . . . . . . . . . . . . 40 42
3. Grant Response . . . . . . . . . . . . . . . . . . . . . . . 40 42
3.1. Request Continuation . . . . . . . . . . . . . . . . . . 42 44
3.2. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 43 45
3.2.1. Single Access Token . . . . . . . . . . . . . . . . . 43 45
3.2.2. Multiple Access Tokens . . . . . . . . . . . . . . . 46 48
3.3. Interaction Modes . . . . . . . . . . . . . . . . . . . . 47 49
3.3.1. Redirection to an arbitrary URL . . . . . . . . . . . 47 49
3.3.2. Launch of an application URL . . . . . . . . . . . . 48 50
3.3.3. Post-interaction Callback to an RC a Client Instance
Accessible URL . . . . . . . 48 . . . . . . . . . . . . 50
3.3.4. Display of a Short User Code . . . . . . . . . . . . 49 51
3.3.5. Extending Interaction Mode Responses . . . . . . . . 50 52
3.4. Returning User Information . . . . . . . . . . . . . . . 50 52
3.5. Returning Dynamically-bound Reference Handles . . . . . . 51 53
3.6. Error Response . . . . . . . . . . . . . . . . . . . . . 53 55
3.7. Extending the Response . . . . . . . . . . . . . . . . . 53 55
4. Interaction at the AS . . . . . . . . . . . . . . . . . . . . 53 55
4.1. Interaction at a Redirected URI . . . . . . . . . . . . . 54 56
4.2. Interaction at the User Code URI . . . . . . . . . . . . 54 56
4.3. Interaction through an Application URI . . . . . . . . . 55 57
4.4. Post-Interaction Completion . . . . . . . . . . . . . . . 55 57
4.4.1. Completing Interaction with a Browser Redirect to the
Callback URI . . . . . . . . . . . . . . . . . . . . 56 57
4.4.2. Completing Interaction with a Direct HTTP Request
Callback . . . . . . . . . . . . . . . . . . . . . . 56 58
4.4.3. Calculating the interaction hash . . . . . . . . . . 57 59
5. Continuing a Grant Request . . . . . . . . . . . . . . . . . 58 60
5.1. Continuing After a Completed Interaction . . . . . . . . 60 62
5.2. Continuing During Pending Interaction . . . . . . . . . . 61 63
5.3. Modifying an Existing Request . . . . . . . . . . . . . . 62 64
5.4. Getting the Current State of a Grant Request . . . . . . 67 69
5.5. Canceling a Grant Request . . . . . . . . . . . . . . . . 68 70
6. Token Management . . . . . . . . . . . . . . . . . . . . . . 68 70
6.1. Rotating the Access Token . . . . . . . . . . . . . . . . 69 71
6.2. Revoking the Access Token . . . . . . . . . . . . . . . . 70 72
7. Using Access Tokens . . . . . . . . . . . . . . . . . . . . . 71 73
8. Binding Keys . . . . . . . . . . . . . . . . . . . . . . . . 72 74
8.1. Detached JWS . . . . . . . . . . . . . . . . . . . . . . 73 75
8.2. Attached JWS . . . . . . . . . . . . . . . . . . . . . . 75 77
8.3. Mutual TLS . . . . . . . . . . . . . . . . . . . . . . . 79 81
8.4. Demonstration of Proof-of-Possession (DPoP) . . . . . . . 81 83
8.5. HTTP Signing . . . . . . . . . . . . . . . . . . . . . . 82 84
8.6. OAuth Proof of Possession (PoP) . . . . . . . . . . . . . 83 85
9. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 85 87
10. Resource Servers . . . . . . . . . . . . . . . . . . . . . . 86 88
10.1. Introspecting a Token . . . . . . . . . . . . . . . . . 86 88
10.2. Deriving a downstream token . . . . . . . . . . . . . . 88 90
10.3. Registering a Resource Handle . . . . . . . . . . . . . 89 91
10.4. Requesting Resources With Insufficient Access . . . . . 91 93
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 91 93
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 91 94
13. Security Considerations . . . . . . . . . . . . . . . . . . . 92 94
14. Privacy Considerations . . . . . . . . . . . . . . . . . . . 92 94
15. Normative References . . . . . . . . . . . . . . . . . . . . 92 94
Appendix A. Document History . . . . . . . . . . . . . . . . . . 94 96
Appendix B. Component Data Models . . . . . . . . . . . . . . . 94 97
Appendix C. Example Protocol Flows . . . . . . . . . . . . . . . 95 97
C.1. Redirect-Based User Interaction . . . . . . . . . . . . . 95 97
C.2. Secondary Device Interaction . . . . . . . . . . . . . . 99 101
Appendix D. No User Involvement . . . . . . . . . . . . . . . . 102 104
D.1. Asynchronous Authorization . . . . . . . . . . . . . . . 103 105
D.2. Applying OAuth 2 Scopes and Client IDs . . . . . . . . . 106 108
Appendix E. JSON Structures and Polymorphism . . . . . . . . . . 107 109
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 108 110

1. Introduction

This protocol allows a piece of software, the resource client, client instance, to
request delegated authorization to resource servers and to request
direct information. This delegation is facilitated by an
authorization server usually on behalf of a resource owner. The
requesting party operating the software may interact with the
authorization server to authenticate, provide consent, and authorize
the request.

The process by which the delegation happens is known as a grant, and
GNAP allows for the negotiation of the grant process over time by
multiple parties acting in distinct roles.

This protocol solves many of the same use cases as OAuth 2.0
[RFC6749], OpenID Connect [OIDC], and the family of protocols that
have grown up around that ecosystem. However, GNAP is not an
extension of OAuth 2.0 and is not intended to be directly compatible
with OAuth 2.0. GNAP seeks to provide functionality and solve use
cases that OAuth 2.0 cannot easily or cleanly address. Even so, GNAP
and OAuth 2.0 will exist in parallel for many deployments, and
considerations have been taken to facilitate the mapping and
transition from legacy systems to GNAP. Some examples of these can
be found in Appendix D.2.

1.1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

1.2. Roles

The parties in GNAP perform actions under different roles. Roles are
defined by the actions taken and the expectations leveraged on the
role by the overall protocol.

Authorization Server (AS) Manages the requested delegations for the
RO. The AS issues tokens and directly delegated information to an
instance of the RC. client. The AS is defined by its grant endpoint,
a single URL that accepts a POST request with a JSON payload. The
AS could also have other endpoints, including interaction
endpoints and user code endpoints, and these are introduced to the
RC as needed during the delegation process.

Resource

Client (RC, aka "client") Requests tokens and directly delegated information from the AS
AS, and uses tokens at the RS. An instance For some kinds of client software,
there could be many instances of a single piece of client
software. This specification differentiates between a specific
instance (the client instance) and the RC software running the
instance (the client software). A client instance is identified
by its unique key, which can be known to the AS prior to the first request.
request or introduced to the AS as part of the protocol. The AS
determines which policies apply to a given
RC, client instance,
including what it can request and on whose behalf.

Resource Server (RS, aka "API") Accepts tokens from the RC client
instance issued by the AS and serves delegated resources on behalf
of the RO. There could be multiple RSs protected by the AS that
the RC client instance will call.

Resource Owner (RO) Authorizes the request from the RC client instance
to the RS, often interactively at the AS.

Requesting Party (RQ, aka "user") Operates and interacts with the
RC.
client instance.

The design of GNAP does not assume any one deployment architecture,
but instead attempts to define roles that can be fulfilled in a
number of different ways for different use cases. As long as a given
role fulfills all of its obligations and behaviors as defined by the
protocol, GNAP does not make additional requirements on its structure
or setup.

Multiple roles can be fulfilled by the same party, and a given party
can switch roles in different instances of the protocol. For
example, the RO and RQ in many instances are the same person, where a
user is authorizing the RC client instance to act on their own behalf at
the RS. In this case, one party fulfills both of the RO and RQ
roles, but the roles themselves are still defined separately from
each other to allow for other use cases where they are fulfilled by
different parties.

For another example, in some complex scenarios, an RS receiving
requests from one RC client instance can act as an RC a client instance for a
downstream secondary RS in order to fulfill the original request. In
this case, one piece of software is both an RS and an RC a client instance
from different perspectives, and it fulfills these roles separately
as far as the overall protocol is concerned.

A single role need not be deployed as a monolithic service. For
example, An RC A client instance could have components that are installed
on the RQ's device as well as a back-end system that it communicates
with. If both of these components participate in the delegation
protocol, they are both considered part of the RC. client instance. If
there are several copies of the client software that run separately
but all share the same key material, such as a deployed cluster, then
this cluster is considered a single client instance.

For another example, an AS could likewise be built out of many
constituent components in a distributed architecture. The component
that the RC client instance calls directly could be different from the
component that the the RO interacts with to drive consent, since API
calls and user interaction have different security considerations in
many environments. Furthermore, the AS could need to collect
identity claims about the RO from one system that deals with user
attributes while generating access tokens at another system that
deals with security rights. From the perspective of GNAP, all of
these are pieces of the AS and together fulfill the role of the AS as
defined by the protocol.

[[ See issue #29 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/29) ]]

[[ See issue #32 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/32) ]]

1.3. Elements

In addition to the roles above, the protocol also involves several
elements that are acted upon by the roles throughout the process.

Access Token A credential representing a set of access rights
delegated to the RC. client instance. The access token is created by
the AS, consumed and verified by the RS, and issued to and carried
by the
RC. client instance. The contents and format of the access
token are opaque to the
RC. client.

Grant The process by which the RC client instance requests and is given
delegated access to the RS by the AS through the authority of the
RO.

Cryptographic Key A cryptographic element binding a request to a
holder of the key. Access tokens and RC client instances can be
associated with specific keys.

Resource A protected API served by the RS and accessed by the RC. client
instance. Access to this resource is delegated by the RO as part
of the grant process.

Subject Information Information about the RO that is returned
directly to the RC client instance from the AS without the RC client
instance making a separate call to an RS. Access to this
information is delegated by the RO as part of the grant process.

[[ See issue #33 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/33) ]]

1.4. Sequences

GNAP can be used in a variety of ways to allow the core delegation
process to take place. Many portions of this process are
conditionally present depending on the context of the deployments,
and not every step in this overview will happen in all circumstances.

Note that a connection between roles in this process does not
necessarily indicate that a specific protocol message is sent across
the wire between the components fulfilling the roles in question, or
that a particular step is required every time. For example, for an
RC a
client instance interested in only getting subject information
directly, and not calling an RS, all steps involving the RS below do
not apply.

In some circumstances, the information needed at a given stage is
communicated out of band or is preconfigured between the components
or entities performing the roles. For example, one entity can fulfil
multiple roles, and so explicit communication between the roles is
not necessary within the protocol flow.

+------------+ +------------+
| Requesting | ~ ~ ~ ~ ~ ~ | Resource |
| Party (RQ) | | Owner (RO) |
+------------+ +------------+
+ +
+ +
(A) (B)
+ +
+ +
+--------+ + +------------+
|Resource|--------------(1)------+------>| Resource |
| Client |--------------(1)------+------>| Resource |
|Instance| + | Server |
| (RC) | +---------------+ | (RS) |
| |--(2)->| Authorization | | |
| |<-(3)--| Server | | |
| | | (AS) | | |
| |--(4)->| | | |
| |<-(5)--| | | |
| |--------------(6)------------->| |
| | | |<~(7)~~| |
| |<-------------(8)------------->| |
| |--(9)->| | | |
| |<-(10)-| | | |
| |--------------(11)------------>| |
| | | |<~(12)~| |
| |-(13)->| | | |
| | | | | |
+--------+ +---------------+ +------------+

Legend
+ + + indicates a possible interaction with a human
----- indicates an interaction between protocol roles
~ ~ ~ indicates a potential equivalence or out-of-band communication between roles

* (A) The RQ interacts with the RC client instance to indicate a need
for resources on behalf of the RO. This could identify the RS the RC
client instance needs to call, the resources needed, or the RO
that is needed to approve the request. Note that the RO and RQ
are often the same entity in practice.

* (1) The RC client instance attempts to call the RS (Section 10.4) to
determine what access is needed. The RS informs the RC client
instance that access can be granted through the AS. Note that for
most situations, the RC client instance already knows which AS to
talk to and which kinds of access it needs.

* (2) The RC client instance requests access at the AS (Section 2).

* (3) The AS processes the request and determines what is needed to
fulfill the request. The AS sends its response to the RC client
instance (Section 3).

* (B) If interaction is required, the AS interacts with the RO
(Section 4) to gather authorization. The interactive component of
the AS can function using a variety of possible mechanisms
including web page redirects, applications, challenge/response
protocols, or other methods. The RO approves the request for the
RC
client instance being operated by the RQ. Note that the RO and RQ
are often the same entity in practice.

* (4) The RC client instance continues the grant at the AS (Section 5).

* (5) If the AS determines that access can be granted, it returns a
response to the RC client instance (Section 3) including an access
token (Section 3.2) for calling the RS and any directly returned
information (Section 3.4) about the RO.

* (6) The RC client instance uses the access token (Section 7) to call
the RS.

* (7) The RS determines if the token is sufficient for the request
by examining the token, potentially calling the AS (Section 10.1).
Note that the RS could also examine the token directly, call an
internal data store, execute a policy engine request, or any
number of alternative methods for validating the token and its
fitness for the request.

* (8) The RC to call client instance calls the RS (Section 7) using the access
token until the RS or RC client instance determine that the token is
no longer valid.

* (9) When the token no longer works, the RC client instance fetches an
updated access token (Section 6.1) based on the rights granted in
(5).

* (10) The AS issues a new access token (Section 3.2) to the RC. client
instance.

* (11) The RC client instance uses the new access token (Section 7) to
call the RS.

* (12) The RS determines if the new token is sufficient for the
request by examining the token, potentially calling the AS
(Section 10.1).

* (13) The RC client instance disposes of the token (Section 6.2) once
the RC client instance has completed its access of the RS and no
longer needs the token.

The following sections and Appendix C contain specific guidance on
how to use GNAP in different situations and deployments.

1.4.1. Redirect-based Interaction

In this example flow, the RC client instance is a web application that
wants access to resources on behalf of the current user, who acts as
both the requesting party (RQ) and the resource owner (RO). Since
the RC client instance is capable of directing the user to an arbitrary
URL and receiving responses from the user's browser, interaction here
is handled through front-channel redirects using the user's browser.
The RC client instance uses a persistent session with the user to ensure
the same user that is starting the interaction is the user that
returns from the interaction.

+--------+ +--------+ +------+
| RC Client | | AS | | RO |
| |
|Instance| | | | + |
| |< (1) + Start Session + + + + + + + + + + + + + + + +| RQ |
| | | | |(User)|
| |--(2)--- Request Access --------->| | | |
| | | | | |
| |<-(3)-- Interaction Needed -------| | | |
| | | | | |
| |+ (4) + Redirect for Interaction + + + + + + + + + > | |
| | | | | |
| | | |<+ (5) +>| |
| | | | AuthN | |
| | | | | |
| | | |<+ (6) +>| |
| | | | AuthZ | |
| | | | | |
| |< (7) + Redirect for Continuation + + + + + + + + + +| |
| | | | +------+
| |--(8)--- Continue Request ------->| |
| | | |
| |<-(9)----- Grant Access ----------| |
| | | |
+--------+ +--------+

1. The RC client instance establishes a verifiable session to the user,
in the role of the RQ.

2. The RC client instance requests access to the resource (Section 2).
The RC client instance indicates that it can redirect to an
arbitrary URL (Section 2.5.1) and receive a callback from the
browser (Section 2.5.3). The RC client instance stores verification
information for its callback in the session created in (1).

3. The AS determines that interaction is needed and responds
(Section 3) with a URL to send the user to (Section 3.3.1) and
information needed to verify the callback (Section 3.3.3) in (7).
The AS also includes information the RC client instance will need to
continue the request (Section 3.1) in (8). The AS associates
this continuation information with an ongoing request that will
be referenced in (4), (6), and (8).

4. The RC client instance stores the verification and continuation
information from (3) in the session from (1). The RC client
instance then redirects the user to the URL (Section 4.1) given
by the AS in (3). The user's browser loads the interaction
redirect URL. The AS loads the pending request based on the
incoming URL generated in (3).

5. The user authenticates at the AS, taking on the role of the RO.

6. As the RO, the user authorizes the pending request from the RC.
client instance.

7. When the AS is done interacting with the user, the AS redirects
the user back (Section 4.4.1) to the RC client instance using the
callback URL provided in (2). The callback URL is augmented with
an interaction reference that the AS associates with the ongoing
request created in (2) and referenced in (4). The callback URL
is also augmented with a hash of the security information
provided in (2) and (3). The RC client instance loads the
verification information from (2) and (3) from the session
created in (1). The RC client instance calculates a hash
(Section 4.4.3) based on this information and continues only if
the hash validates. Note that the RC client instance needs to
ensure that the parameters for the incoming request match those
that it is expecting from the session created in (1). The RC client
instance also needs to be prepared for the RQ never being
returned to the RC client instance and handle time outs
appropriately.

8. The RC client instance loads the continuation information from (3)
and sends the interaction reference from (7) in a request to
continue the request (Section 5.1). The AS validates the
interaction reference ensuring that the reference is associated
with the request being continued.

9. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and direct
subject information (Section 3.4) to the RC. client instance.

An example set of protocol messages for this method can be found in
Appendix C.1.

1.4.2. User-code Interaction

In this example flow, the RC client instance is a device that is capable
of presenting a short, human-readable code to the user and directing
the user to enter that code at a known URL. The RC client instance is
not capable of presenting an arbitrary URL to the user, nor is it
capable of accepting incoming HTTP requests from the user's browser.
The RC client instance polls the AS while it is waiting for the RO to
authorize the request. The user's interaction is assumed to occur on
a secondary device. In this example it is assumed that the user is
both the RQ and RO, though the user is not assumed to be interacting
with the RC client instance through the same web browser used for
interaction at the AS.

+--------+ +--------+ +------+
| RC Client | | AS | | RO |
| |--(1)---
|Instance|--(1)--- Request Access --------->| | | + |
| | | | | RQ |
| |<-(2)-- Interaction Needed -------| | |(User)|
| | | | | |
| |+ (3) + + Display User Code + + + + + + + + + + + + >| |
| | | | | |
| | | |<+ (4) + | |
| | | |Open URI | |
| | | | | |
| | | |<+ (5) +>| |
| | | | AuthN | |
| |--(9)--- Continue Request (A) --->| | | |
| | | |<+ (6) +>| |
| |<-(10)- Not Yet Granted (Wait) ---| | Code | |
| | | | | |
| | | |<+ (7) +>| |
| | | | AuthZ | |
| | | | | |
| | | |<+ (8) +>| |
| | | |Completed| |
| | | | | |
| |--(11)-- Continue Request (B) --->| | +------+
| | | |
| |<-(12)----- Grant Access ---------| |
| | | |
+--------+ +--------+

1. The RC client instance requests access to the resource (Section 2).
The RC client instance indicates that it can display a user code
(Section 2.5.4).

2. The AS determines that interaction is needed and responds
(Section 3) with a user code to communicate to the user
(Section 3.3.4). This could optionally include a URL to direct
the user to, but this URL should be static and so could be
configured in the RC's client instance's documentation. The AS also
includes information the RC client instance will need to continue
the request (Section 3.1) in (8) and (10). The AS associates
this continuation information with an ongoing request that will
be referenced in (4), (6), (8), and (10).

3. The RC client instance stores the continuation information from (2)
for use in (8) and (10). The RC client instance then communicates
the code to the user (Section 4.1) given by the AS in (2).

4. The user's directs their browser to the user code URL. This URL
is stable and can be communicated via the RC's client software's
documentation, the AS documentation, or the RC client software
itself. Since it is assumed that the RO will interact with the
AS through a secondary device, the RC client instance does not
provide a mechanism to launch the RO's browser at this URL.

5. The RQ authenticates at the AS, taking on the role of the RO.

6. The RO enters the code communicated in (3) to the AS. The AS
validates this code against a current request in process.

7. As the RO, the user authorizes the pending request from the RC.
client instance.

8. When the AS is done interacting with the user, the AS indicates
to the RO that the request has been completed.

9. Meanwhile, the RC client instance loads the continuation
information stored at (3) and continues the request (Section 5).
The AS determines which ongoing access request is referenced
here and checks its state.

10. If the access request has not yet been authorized by the RO in
(6), the AS responds to the RC client instance to continue the
request (Section 3.1) at a future time through additional polled
continuation requests. This response can include updated
continuation information as well as information regarding how
long the RC client instance should wait before calling again. The RC
client instance replaces its stored continuation information
from the previous response (2). Note that the AS may need to
determine that the RO has not approved the request in a
sufficient amount of time and return an appropriate error to the RC.
client instance.

11. The RC client instance continues to poll the AS (Section 5.2) with
the new continuation information in (9).

12. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the RC. client instance.

An example set of protocol messages for this method can be found in
Appendix C.2.

1.4.3. Asynchronous Authorization

In this example flow, the RQ and RO roles are fulfilled by different
parties, and the RO does not interact with the RC. client instance. The
AS reaches out asynchronously to the RO during the request process to
gather the RO's authorization for the RC's client instance's request. The RC
client instance polls the AS while it is waiting for the RO to
authorize the request.

+--------+ +--------+ +------+
| RC Client | | AS | | RO |
| |--(1)---
|Instance|--(1)--- Request Access --------->| | | |
| | | | | |
| |<-(2)-- Not Yet Granted (Wait) ---| | | |
| | | |<+ (3) +>| |
| | | | AuthN | |
| |--(6)--- Continue Request (A) --->| | | |
| | | |<+ (4) +>| |
| |<-(7)-- Not Yet Granted (Wait) ---| | AuthZ | |
| | | | | |
| | | |<+ (5) +>| |
| | | |Completed| |
| | | | | |
| |--(8)--- Continue Request (B) --->| | +------+
| | | |
| |<-(9)------ Grant Access ---------| |
| | | |
+--------+ +--------+

1. The RC client instance requests access to the resource (Section 2).
The RC client instance does not send any interactions modes to the
server, indicating that it does not expect to interact with the
RO. The RC client instance can also signal which RO it requires
authorization from, if known, by using the user request section
(Section 2.4).

2. The AS determines that interaction is needed, but the RC client
instance cannot interact with the RO. The AS responds
(Section 3) with the information the RC client instance will need to
continue the request (Section 3.1) in (6) and (8), including a
signal that the RC client instance should wait before checking the
status of the request again. The AS associates this continuation
information with an ongoing request that will be referenced in
(3), (4), (5), (6), and (8).

3. The AS determines which RO to contact based on the request in
(1), through a combination of the user request (Section 2.4), the
resources request (Section 2.1), and other policy information.
The AS contacts the RO and authenticates them.

4. The RO authorizes the pending request from the RC. client instance.

5. When the AS is done interacting with the RO, the AS indicates to
the RO that the request has been completed.

6. Meanwhile, the RC client instance loads the continuation information
stored at (3) and continues the request (Section 5). The AS
determines which ongoing access request is referenced here and
checks its state.

7. If the access request has not yet been authorized by the RO in
(6), the AS responds to the RC client instance to continue the
request (Section 3.1) at a future time through additional
polling. This response can include refreshed credentials as well
as information regarding how long the RC client instance should wait
before calling again. The
RC client instance replaces its stored
continuation information from the previous response (2). Note
that the AS may need to determine that the RO has not approved
the request in a sufficient amount of time and return an
appropriate error to the RC. client instance.

8. The RC client instance continues to poll the AS (Section 5.2) with
the new continuation information from (7).

9. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and direct
subject information (Section 3.4) to the RC. client instance.

An example set of protocol messages for this method can be found in
Appendix D.1.

1.4.4. Software-only Authorization

In this example flow, the AS policy allows the RC client instance to
make a call on its own behalf, without the need for a RO to be
involved at runtime to approve the decision. Since there is no
explicit RO, the RC client instance does not interact with an RO.

+--------+ +--------+
| RC Client | | AS |
| |--(1)---
|Instance|--(1)--- Request Access --------->| |
| | | |
| |<-(2)---- Grant Access -----------| |
| | | |
+--------+ +--------+

1. The RC client instance requests access to the resource (Section 2).
The RC client instance does not send any interactions modes to the
server.

2. The AS determines that the request is been authorized, the AS
grants access to the information in the form of access tokens
(Section 3.2) and direct subject information (Section 3.4) to the
RC.
client instance.

An example set of protocol messages for this method can be found in
Appendix D.

1.4.5. Refreshing an Expired Access Token

In this example flow, the RC client instance receives an access token to
access a resource server through some valid GNAP process. The RC client
instance uses that token at the RS for some time, but eventually the
access token expires. The RC client instance then gets a new access
token by rotating the expired access token at the AS using the
token's management URL.

+--------+ +--------+
| RC Client | | AS |
| |--(1)---
|Instance|--(1)--- Request Access ----------------->| |
| | | |
| |<-(2)--- Grant Access --------------------| |
| | | |
| | +--------+ | |
| |--(3)--- Access Resource --->| RS | | |
| | | | | |
| |<-(4)--- Error Response -----| | | |
| | +--------+ | |
| | | |
| |--(5)--- Rotate Token ------------------->| |
| | | |
| |<-(6)--- Rotated Token -------------------| |
| | | |
+--------+ +--------+

1. The RC client instance requests access to the resource (Section 2).

2. The AS grants access to the resource (Section 3) with an access
token (Section 3.2) usable at the RS. The access token response
includes a token management URI.

3. The RC client instance presents the token (Section 7) to the RS.
The RS validates the token and returns an appropriate response
for the API.

4. When the access token is expired, the RS responds to the RC client
instance with an error.

5. The RC client instance calls the token management URI returned in
(2) to rotate the access token (Section 6.1). The RC client
instance presents the access token as well as the appropriate
key.

6. The AS validates the rotation request including the signature and
keys presented in (5) and returns a new access token
(Section 3.2.1). The response includes a new access token and
can also include updated token management information, which the
RC
client instance will store in place of the values returned in
(2).

2. Requesting Access

To start a request, the RC client instance sends JSON [RFC8259] document
with an object as its root. Each member of the request object
represents a different aspect of the RC's client instance's request. Each
field is described in detail in a section below.

resources (object / array of objects/strings) Describes the rights
that the RC client instance is requesting for one or more access
tokens to be used at RS's. Section 2.1

subject (object) Describes the information about the RO that the RC
client instance is requesting to be returned directly in the
response from the AS. Section 2.2

client (object / string) Describes the RC client instance that is
making this request, including the key that the RC client instance
will use to protect this request and any continuation requests at
the AS and any user-
facing user-facing information about the RC client instance
used in interactions at the AS. Section 2.3

user (object / string) Identifies the RQ to the AS in a manner that
the AS can verify, either directly or by interacting with the RQ
to determine their status as the RO. Section 2.4

interact (object) Describes the modes that the RC client instance has
for allowing the RO to interact with the AS and modes for the RC
client instance to receive updates when interaction is complete.
Section 2.5

capabilities (array of strings) Identifies named extension
capabilities that the RC client instance can use, signaling to the AS
which extensions it can use. Section 2.6

existing_grant (string) Identifies a previously-existing grant that
the RC client instance is extending with this request. Section 2.7

claims (object) Identifies the identity claims to be returned as
part of an OpenID Connect claims request. Section 2.8

Additional members of this request object can be defined by
extensions to this protocol as described in Section 2.9 2.8

A non-normative example of a grant request is below:

{
"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
],
"client": {
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
},
"key": {
"proof": "jwsd",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeL...."
}
}
},
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"capabilities": ["ext1", "ext2"],
"subject": {
"sub_ids": ["iss_sub", "email"],
"assertions": ["id_token"]
}
}

The request MUST be sent as a JSON object in the body of the HTTP
POST request with Content-Type "application/json", unless otherwise
specified by the signature mechanism.

2.1. Requesting Resources

If the RC client instance is requesting one or more access tokens for
the purpose of accessing an API, the RC client instance MUST include a
"resources" field. This field MUST be an array (for a single access
token (Section 2.1.1)) or an object (for multiple access tokens
(Section 2.1.3)), as described in the following sections.

2.1.1. Requesting a Single Access Token

When requesting an access token, the RC client instance MUST send a
"resources" field containing a JSON array. The elements of the JSON
array represent rights of access that the RC client instance is
requesting in the access token. The requested access is the sum union of
all elements within the array.

The RC client instance declares what access it wants to associated associate with
the resulting access token using objects that describe multiple
dimensions of access. Each object contains a "type" property that
determines the type of API that the RC client instance is calling.

type (string) The type of resource request as a string. This field
MAY define which other fields are allowed in the request object.
This field is REQUIRED.

The value of this field is under the control of the AS. This field
MUST be compared using an exact byte match of the string value
against known types by the AS. The AS MUST ensure that there is no
collision between different authorization data types that it
supports. The AS MUST NOT do any collation or normalization of data
types during comparison. It is RECOMMENDED that designers of
general-purpose APIs use a URI for this field to avoid collisions
between multiple API types protected by a single AS.

While it is expected that many APIs will have its own properties, a
set of common properties are defined here. Specific API
implementations SHOULD NOT re-use these fields with different
semantics or syntax. The available values for these properties are
determined by the API being protected at the RS.

[[ See issue #34 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/34) ]]

actions (array of strings) The types of actions the RC client instance
will take at the RS as an array of strings. For example, an RC asking a client
instance asking for a combination of "read" and "write" access.

locations (array of strings) The location of the RS as an array of
strings. These strings are typically URIs identifying the
location of the RS.

datatypes (array of strings) The kinds of data available to the RC
client instance at the RS's API as an array of strings. For
example, an RC a client instance asking for access to raw "image" data
and "metadata" at a photograph API.

identifier (string) A string identifier indicating a specific
resource at the RS. For example, a patient identifier for a
medical API or a bank account number for a financial API.

The following non-normative example is asking for three kinds of
access (read, write, delete) to each of two different locations and
two different data types (metadata, images) for a single access token
using the fictitious "photo-api" type definition.

"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}
]

The access requested for a given object when using these fields is
the cross-product of all fields of the object. That is to say, the
object represents a request for all "action" values listed within the
object to be used at all "locations" values listed within the object
for all "datatype" values listed within the object. Assuming the
request above was granted, the RC could assume that it would be able
to do a "read" action against the "images" on the first server as
well as a "delete" action on the "metadata" of the second server, or
any other combination of these fields, using the same access token.

To request a different combination of access, such as requesting one
"action" against one "location" and a different "action" against a
different "location", the RC can include multiple separate objects in
the "resources" array. The following non-normative example uses the
same fictitious "photo-api" type definition to request a single
access token with more specifically targeted access rights by using
two discrete objects within the request.

"resources": [
{
"type": "photo-api",
"actions": [
"read"
],
"locations": [
"https://server.example.net/"
],
"datatypes": [
"images"
]
},
{
"type": "photo-api",
"actions": [
"write",
"delete"
],
"locations": [
"https://resource.local/other"
],
"datatypes": [
"metadata"
]
}
]

The access requested here is for "read" access to "images" on one
server while simultaneously requesting "write" and "delete" access
for "metadata" on a different server, but importantly without
requesting "write" or "delete" access to "images" on the first
server.

It is anticipated that API designers will use a combination of common
fields defined in this specification as well as fields specific to
the API itself. The following non-normative example shows the use of
both common and API-specific fields as part of two different access
fictitious API "type" values. The first access request includes the
"actions", "locations", and "datatypes" fields specified here as well
as the API-specific "geolocation" field. The second access request
includes the "actions" and "identifier" fields specified here as well
as the API-specific "currency" field.

"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
"write"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
],
"geolocation": [
{ lat: -32.364, lng: 153.207 },
{ lat: -35.364, lng: 158.207 }
]
},
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
}
]

If this request is approved, the resulting access token
(Section 3.2.1) 3.2.1)'s access rights will include be the sum of both union of the requested
types of access. access for each of the two APIs, just as above.

2.1.2. Requesting Resources By Reference

Instead of sending an object describing the requested resource
(Section 2.1.1), a RC client instance MAY send a string known to the AS
or RS representing the access being requested. Each string SHOULD
correspond to a specific expanded object representation at the AS.

[[ See issue #35 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/35) ]]

"resources": [
"read", "dolphin-metadata", "some other thing"
]

This value is opaque to the RC client instance and MAY be any valid JSON
string, and therefore could include spaces, unicode characters, and
properly escaped string sequences. However, in some situations the
value is intended to be seen and understood be by the RC client software's
developer. In such cases, the API designer choosing any such human-readable human-
readable strings SHOULD take steps to ensure the string values are
not easily confused by a developer developer, such as by limiting the strings
to easily disambiguated characters.

This functionality is similar in practice to OAuth 2's "scope"
parameter [RFC6749], where a single string represents the set of
access rights requested by the RC. client instance. As such, the
reference string could contain any valid OAuth 2 scope value as in
Appendix D.2. Note that the reference string here is not bound to
the same character restrictions as in OAuth 2's "scope" definition.

A single "resources" array MAY include both object-type and string-
type resource items. In this non-normative example, the RC is
requesting access to a "photo-api" and "financial-transaction" API
type as well as the reference values of "read", "dolphin-metadata",
and "some other thing".

"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read",
"dolphin-metadata",
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
},
"some other thing"
]

[[ See issue #36 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/36) ]]

The requested access is the union of all elements of the array,
including both objects and reference strings.

2.1.3. Requesting Multiple Access Tokens

When requesting multiple access tokens, the resources field is a JSON
object. The names of the JSON object fields are token identifiers
chosen by the RC, client instance, and MAY be any valid string. The
values of the JSON object fields are JSON arrays representing a
single access token request, as specified in requesting a single
access token (Section 2.1.1).

The following non-normative example shows a request for two separate
access tokens, "token1" and "token2".

"resources": {
"token1": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
],
"token2": [
{
"type": "walrus-access",
"actions": [
"foo",
"bar"
],
"locations": [
"https://resource.other/"
],
"datatypes": [
"data",
"pictures",
"walrus whiskers"
]
}
]
}

Any approved access requests are returned in the multiple access
token response (Section 3.2.2) structure using the token identifiers
in the request.

2.1.4. Signaling Token Behavior

While the AS is ultimately in control of how tokens are returned and
bound to the RC, client instance, sometimes the RC client instance has
context about what it can support that can affect the AS's response.
This specification defines several flags that are passed as resource
reference strings (Section 2.1.2).

Each flag applies only to the single resource request in which it
appears.

Support of all flags is optional, such as any other resource
reference value.

multi_token The RC client instance wishes to support multiple
simultaneous access tokens through the token rotation process.
When the RC client instance rotates an access token (Section 6.1),
the AS does not invalidate the previous access token. The old
access token continues to remain valid until such time as it
expires or is revoked through other means.

split_token The RC client instance is capable of receiving multiple
access tokens (Section 3.2.2) in response to any single token
request (Section 2.1.1), or receiving a different number of tokens
than specified in the multiple token request (Section 2.1.3). The
labels of the returned additional tokens are chosen by the AS.
The RC client instance MUST be able to tell from the token response
where and how it can use each of the access tokens. [[ See issue
#37 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/37)
]]

bind_token The RC client instance wants the issued access token to be
bound to the key the RC client instance used (Section 2.3.2) to make
the request. The resulting access token MUST be bound using the
same "proof" mechanism used by the client instance with a "key"
value of "true", indicating the client's client instance's presented key is
to be used for binding. [[ See issue #38 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/38) (https://github.com/
ietf-wg-gnap/gnap-core-protocol/issues/38) ]]

The AS MUST respond with any applied flags in the token response
(Section 3.2) "resources" section.

In this non-normative example, the requested access token is to be
bound to the client's client instance's key and should be kept during
rotation.

"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read",
"bind_token",
"multi_token"
]

Additional flags can be registered in a registry TBD (Section 12).

[[ See issue #39 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/39) ]]

2.2. Requesting User Information

If the RC client instance is requesting information about the RO from
the AS, it sends a "subject" field as a JSON object. This object MAY
contain the following fields (or additional fields defined in a
registry TBD (Section 12)).

sub_ids (array of strings) An array of subject identifier subject
types requested for the RO, as defined by
[I-D.ietf-secevent-subject-identifiers].

assertions (array of strings) An array of requested assertion
formats. Possible values include "id_token" for an [OIDC] ID
Token and "saml2" for a SAML 2 assertion. Additional assertion
values are defined by a registry TBD (Section 12). [[ See issue
#41 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/41)
]]

"subject": {
"sub_ids": [ "iss_sub", "email" ],
"assertions": [ "id_token", "saml2" ]
}

The AS can determine the RO's identity and permission for releasing
this information through interaction with the RO (Section 4), AS
policies, or assertions presented by the RC client instance
(Section 2.4). If this is determined positively, the AS MAY return
the RO's information in its response (Section 3.4) as requested.

Subject identifiers requested by the RC client instance serve only to
identify the RO in the context of the AS and can't be used as
communication channels by the RC, client instance, as discussed in
Section 3.4. One method of requesting
communication channels and other identity claims are discussed in
Section 2.8.

The AS SHOULD NOT re-use subject identifiers for multiple different
ROs.

[[ See issue #42 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/42) ]]

Note: the "sub_ids" and "assertions" request fields are independent
of each other, and a returned assertion MAY omit a requested subject
identifier.

[[ See issue #43 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/43) ]]

2.3. Identifying the RC Client Instance

When sending a non-continuation request to the AS, the RC client
instance MUST identify itself by including the "client" field of the
request and by signing the request as described in Section 8. Note
that for a continuation request (Section 5), the RC client instance is
identified by its association with the request being continued and so
this field is not sent under those circumstances.

When RC client instance information is sent by value, the "client" field
of the request consists of a JSON object with the following fields.

key (object / string) The public key of the RC client instance to be
used in this request as described in Section 2.3.2. This field is
REQUIRED.

class_id (string) An identifier string that the AS can use to
identify the client software comprising this instance of the RC. client instance. The
contents and format of this field are up to the AS. This field is
OPTIONAL.

display (object) An object containing additional information that
the AS MAY display to the RO during interaction, authorization,
and management. This field is OPTIONAL.

"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
},
"cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
},
"class_id": "web-server-1234",
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
}
}

Additional fields are defined in a registry TBD (Section 12).

The RC client instance MUST prove possession of any presented key by the
"proof" mechanism associated with the key in the request. Proof
types are defined in a registry TBD (Section 12) and an initial set
of methods is described in Section 8.

Note that the AS MAY know the RC's client instance's public key ahead of
time, and the AS MAY apply different policies to the request
depending on what has been registered against that key. If the same
public key is sent by value on subsequent access requests, the AS
SHOULD treat these requests as coming from the same RC software client instance
for purposes of identification, authentication, and policy
application. If the AS does not know the RC's client instance's public
key ahead of time, the AS MAY accept or reject the request based on
AS policy, attestations within the client "client" request, and other
mechanisms.

[[ See issue #44 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/44) ]]

2.3.1. Identifying the RC Client Instance

If the RC client instance has an instance identifier that the AS can use
to determine appropriate key information, the RC client instance can
send this value in the "instance_id" field. The instance identifier
MAY be assigned to an
RC a client instance at runtime through the
Section 3.5 or MAY be obtained in another fashion, such as a static
registration process at the AS.

instance_id (string) An identifier string that the AS can use to
identify the particular instance of this RC. client software. The
content and structure of this identifier is opaque to the RC. client
instance.

"client": {
"instance_id": "client-541-ab"
}

If there are no additional fields to send, the RC client instance MAY
send the instance identifier as a direct reference value in lieu of
the object.

"client": "client-541-ab"

When the AS receives a request with an instance identifier, the AS
MUST ensure that the key used to sign the request (Section 8) is
associated with the instance identifier.

If the "instance_id" field is sent, it MUST NOT be accompanied by
other fields unless such fields are explicitly marked safe for
inclusion alongside the instance identifier.

[[ See issue #45 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/45) ]]

If the AS does not recognize the instance identifier, the request
MUST be rejected with an error.

If the RC client instance is identified in this manner, the registered
key for the RC client instance MAY be a symmetric key known to the AS.
The RC client instance MUST NOT send a symmetric key by value in the
request, as doing so would expose the key directly instead of proving
possession of it.

[[ See issue #46 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/46) ]]

2.3.2. Identifying the RC Client Instance Key

The RC client instance key MUST be a public key in at least one
supported format and MUST be applicable to the proofing mechanism
used in the request. If the key is sent in multiple formats, all the
keys MUST be the same. The key presented in this field MUST be the
key used to sign the request.

proof (string) The form of proof that the RC client instance will use
when presenting the key to the AS. The valid values of this field
and the processing requirements for each are detailed in
Section 8. This field is REQUIRED.

jwk (object) Value of the public key as a JSON Web Key. MUST contain
an "alg" field which is used to validate the signature. MUST
contain the "kid" field to identify the key in the signed object.

cert (string) PEM serialized value of the certificate used to sign
the request, with optional internal whitespace.

cert#S256 (string) The certificate thumbprint calculated as per
OAuth-MTLS [RFC8705] in base64 URL encoding.

Additional key types are defined in a registry TBD (Section 12).

[[ See issue #47 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/47) ]]

This non-normative example shows a single key presented in multiple
formats using a single proofing mechanism.

"key": {
"proof": "jwsd",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
},
"cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
}

Continuation requests (Section 5) MUST use the same key (or its most
recent rotation) and proof method as the initial request.

2.3.3. Providing Displayable RC Client Instance Information

If the RC client instance has additional information to display to the
RO during any interactions at the AS, it MAY send that information in
the "display" field. This field is a JSON object that declares
information to present to the RO during any interactive sequences.

name (string) Display name of the RC client software

uri (string) User-facing web page of the RC client software

logo_uri (string) Display image to represent the RC client software

"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
}

[[ See issue #48 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/48) ]]

Additional display fields are defined by a registry TBD (Section 12).

The AS SHOULD use these values during interaction with the RO. The
values are for informational purposes only and MUST NOT be taken as
authentic proof of the RC's client instance's identity or source. The AS
MAY restrict display values to specific RC client instances, as
identified by their keys in Section 2.3.

2.3.4. Authenticating the RC Client Instance

If the presented key is known to the AS and is associated with a
single instance of the RC client software, the process of presenting a
key and proving possession of that key is sufficient to authenticate
the
RC client instance to the AS. The AS MAY associate policies with
the RC software client instance identified by this key, such as limiting which
resources can be requested and which interaction methods can be used.
For example, only specific RCs client instances with certain known keys
might be trusted with access tokens without the AS interacting
directly with the RO as in Appendix D.

The presentation of a key allows the AS to strongly associate
multiple successive requests from the same RC client instance with each
other. This is true when the AS knows the key ahead of time and can
use the key to authenticate the RC software, client instance, but also if the key
is ephemeral and created just for this series of requests. As such
the AS MAY allow for RCs client instances to make requests with unknown
keys. This pattern allows for ephemeral RCs, client instances, such as
single-page applications, and RCs client software with many individual
long-lived instances, such as mobile applications, to generate their
own key
pairs per instance and use them the keys within the protocol without
having to go through a separate registration step. The AS MAY limit
which capabilities are made available to RCs client instances with
unknown keys. For example, the AS could have a policy saying that
only previously-
registered RCs previously-registered client instances can request particular
resources, or that all RCs client instances with unknown keys have to be
interactively approved by an RO.

2.4. Identifying the User

If the RC client instance knows the identity of the RQ through one or
more identifiers or assertions, the RC client instance MAY send that
information to the AS in the "user" field. The RC client instance MAY
pass this information by value or by reference.

sub_ids (array of strings) An array of subject identifiers for the
RQ, as defined by [I-D.ietf-secevent-subject-identifiers].

assertions (object) An object containing assertions as values keyed
on the assertion type defined by a registry TBD (Section 12).
Possible keys include "id_token" for an [OIDC] ID Token and
"saml2" for a SAML 2 assertion. Additional assertion values are
defined by a registry TBD (Section 12). [[ See issue #41
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/41) ]]

"user": {
"sub_ids": [ {
"subject_type": "email",
"email": "user@example.com"
} ],
"assertions": {
"id_token": "eyj..."
}
}

Subject identifiers are hints to the AS in determining the RO and
MUST NOT be taken as declarative statements that a particular RO is
present at the RC client instance and acting as the RQ. Assertions
SHOULD be validated by the AS. [[ See issue #49 (https://github.com/ietf-wg-
gnap/gnap-core-protocol/issues/49) (https://github.com/
ietf-wg-gnap/gnap-core-protocol/issues/49) ]]

If the identified RQ does not match the RO present at the AS during
an interaction step, the AS SHOULD reject the request with an error.

[[ See issue #50 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/50) ]]
If the AS trusts the RC client instance to present verifiable
assertions, the AS MAY decide, based on its policy, to skip
interaction with the RO, even if the RC client instance provides one or
more interaction modes in its request.

2.4.1. Identifying the User by Reference

User reference identifiers can be dynamically issued by the AS
(Section 3.5) to allow the RC client instance to represent the same RQ
to the AS over subsequent requests.

If the RC client instance has a reference for the RQ at this AS, the RC
client instance MAY pass that reference as a string. The format of
this string is opaque to the
RC. client instance.

"user": "XUT2MFM1XBIKJKSDU8QM"

User reference identifiers are not intended to be human-readable user
identifiers or structured assertions. For the RC client instance to
send either of these, use the full user request object (Section 2.4)
instead.

[[ See issue #51 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/51) ]]

If the AS does not recognize the user reference, it MUST return an
error.

2.5. Interacting with the User

Many times, the AS will require interaction with the RO in order to
approve a requested delegation to the RC client instance for both
resources and direct claim information. Many times the RQ using the RC
client instance is the same person as the RO, and the RC client instance
can directly drive interaction with the AS by redirecting the RQ on
the same device, or by launching an application. Other times, the RC
client instance can provide information to start the RO's interaction
on a secondary device, or the RC client instance will wait for the RO to
approve the request asynchronously. The RC client instance could also
be signaled that interaction has completed by the AS making
callbacks. To facilitate all of these modes, the RC client instance
declares the means that it can interact using the "interact" field.

The "interact" field is a JSON object with keys that declare
different interaction modes. A RC client instance MUST NOT declare an
interaction mode it does not support. The RC client instance MAY send
multiple modes in the same request. There is no preference order
specified in this request. An AS MAY respond to any, all, or none of
the presented interaction modes (Section 3.3) in a request, depending
on its capabilities and what is allowed to fulfill the request. This
specification defines the following interaction modes:

redirect (boolean) Indicates that the RC client instance can direct the
RQ to an arbitrary URL at the AS for interaction. Section 2.5.1

app (boolean) Indicates that the RC client instance can launch an
application on the RQ's device for interaction. Section 2.5.2

callback (object) Indicates that the RC client instance can receive a
callback from the AS after interaction with the RO has concluded.
Section 2.5.3

user_code (boolean) Indicates that the RC client instance can
communicate a human-
readable human-readable short code to the RQ for use with a
stable URL at the AS. Section 2.5.4

ui_locales (array of strings) Indicates the RQ's preferred locales
that the AS can use during interaction, particularly before the RO
has authenticated. Section 2.5.5

The following sections detail requests for interaction modes.
Additional interaction modes are defined in a registry TBD
(Section 12).

[[ See issue #52 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/52) ]]

In this non-normative example, the RC client instance is indicating that
it can redirect (Section 2.5.1) the RQ to an arbitrary URL and can
receive a callback (Section 2.5.3) through a browser request.

"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}

In this non-normative example, the RC client instance is indicating that
it can display a user code (Section 2.5.4) and direct the RQ to an
arbitrary URL of maximum length (Section 2.5.1.1) 255 characters, 2.5.1) on a secondary device, but it cannot
accept a callback.

"interact": {
"redirect": 255, true,
"user_code": true
}

If the RC client instance does not provide a suitable interaction
mechanism, the AS cannot contact the RO asynchronously, and the AS
determines that interaction is required, then the AS SHOULD return an
error since the
RC client instance will be unable to complete the
request without authorization.

The AS SHOULD apply suitable timeouts to any interaction mechanisms
provided, including user codes and redirection URLs. The RC client
instance SHOULD apply suitable timeouts to any callback URLs.

2.5.1. Redirect to an Arbitrary URL

If the RC client instance is capable of directing the RQ to a URL
defined by the AS at runtime, the RC client instance indicates this by
sending the "redirect" field with the boolean value "true". The
means by which the RC client instance will activate this URL is out of
scope of this specification, but common methods include an HTTP
redirect, launching a browser on the RQ's
device, providing a scannable image encoding, and printing out a URL
to an interactive console.

"interact": {
"redirect": true
}

If this interaction mode is supported for this RC and request, the AS
returns a redirect interaction response Section 3.3.1.

2.5.1.1. Redirect to an Arbitrary Shortened URL

If the RC would prefer to redirect to a shortened URL defined by the
AS at runtime, the RC indicates this by sending the "redirect" field
with an integer indicating the maximum character length of the
returned URL. The AS MAY use this value to decide whether to return
a shortened form of the response URL. If browser on the AS cannot shorten its
response RQ's device, providing a
scannable image encoding, and printing out a URL enough to fit in the requested size, the AS SHOULD
return an error. [[ See issue #53 (https://github.com/ietf-wg-gnap/
gnap-core-protocol/issues/53) ]] interactive
console.

"interact": {
"redirect": 255 true
}

If this interaction mode is supported for this RC client instance and
request, the AS returns a redirect interaction response with short URL
Section 3.3.1.

2.5.2. Open an Application-specific URL

If the RC client instance can open a URL associated with an application
on the RQ's device, the RC client instance indicates this by sending the
"app" field with boolean value "true". The means by which the RC client
instance determines the application to open with this URL are out of
scope of this specification.

"interact": {
"app": true
}

If this interaction mode is supported for this RC client instance and
request, the AS returns an app interaction response with an app URL
payload Section 3.3.2.

[[ See issue #54 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/54) ]]

2.5.3. Receive a Callback After Interaction

If the RC client instance is capable of receiving a message from the AS
indicating that the RO has completed their interaction, the RC client
instance indicates this by sending the "callback" field. The value
of this field is an object containing the following members.

uri (string) REQUIRED. Indicates the URI to send the RO to after
interaction. This URI MAY be unique per request and MUST be
hosted by or accessible by the RC. client instance. This URI MUST NOT
contain any fragment component. This URI MUST be protected by
HTTPS, be hosted on a server local to the RO's browser
("localhost"), or use an application-specific URI scheme. If the RC
client instance needs any state information to tie to the front
channel interaction response, it MUST use a unique callback URI to
link to that ongoing state. The allowable URIs and URI patterns
MAY be restricted by the AS based on the RC's client instance's
presented key information. The callback URI SHOULD be presented
to the RO during the interaction phase before redirect. [[ See
issue #55 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/55) (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/55) ]]

nonce (string) REQUIRED. Unique value to be used in the calculation
of the "hash" query parameter sent to the callback URL, must be
sufficiently random to be unguessable by an attacker. MUST be
generated by the RC client instance as a unique value for this
request.

method (string) REQUIRED. The callback method that the AS will use
to contact the RC. client instance. Valid values include "redirect"
Section 2.5.3.1 and "push" Section 2.5.3.2, with other values
defined by a registry TBD (Section 12).

hash_method (string) OPTIONAL. The hash calculation mechanism to be
used for the callback hash in Section 4.4.3. Can be one of "sha3"
or "sha2". If absent, the default value is "sha3". [[ See issue
#56 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/56)
]]

"interact": {
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
If this interaction mode is supported for this RC client instance and
request, the AS returns a nonce for use in validating the callback
response (Section 3.3.3). Requests to the callback URI MUST be
processed as described in Section 4.4, and the AS MUST require
presentation of an interaction callback reference as described in
Section 5.1.

[[ See issue #58 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/58) ]]

[[ See issue #59 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/59) ]]

2.5.3.1. Receive an HTTP Callback Through the Browser

A callback "method" value of "redirect" indicates that the RC client
instance will expect a call from the RO's browser using the HTTP
method GET as described in Section 4.4.1.

"interact": {
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}

Requests to the callback URI MUST be processed by the RC client instance
as described in Section 4.4.1.

Since the incoming request to the callback URL is from the RO's
browser, this method is usually used when the RO and RQ are the same
entity. As such, the RC client instance MUST ensure the RQ is present
on the request to prevent substitution attacks.

2.5.3.2. Receive an HTTP Direct Callback

A callback "method" value of "push" indicates that the RC client
instance will expect a call from the AS directly using the HTTP
method POST as described in Section 4.4.2.

"interact": {
"callback": {
"method": "push",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
Requests to the callback URI MUST be processed by the RC client instance
as described in Section 4.4.2.

Since the incoming request to the callback URL is from the AS and not
from the RO's browser, the RC client instance MUST NOT require the RQ to
be present on the incoming HTTP request.

[[ See issue #60 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/60) ]]

2.5.4. Display a Short User Code

If the RC client instance is capable of displaying or otherwise
communicating a short, human-entered code to the RO, the RC client
instance indicates this by sending the "user_code" field with the
boolean value "true". This code is to be entered at a static URL
that does not change at runtime, as described in Section 3.3.4.

"interact": {
"user_code": true
}

If this interaction mode is supported for this RC client instance and
request, the AS returns a user code and interaction URL as specified
in Section 4.2.

2.5.5. Indicate Desired Interaction Locales

If the RC client instance knows the RQ's locale and language
preferences, the RC client instance can send this information to the AS
using the "ui_locales" field with an array of locale strings as
defined by [RFC5646].

"interact": {
"ui_locales": ["en-US", "fr-CA"]
}

If possible, the AS SHOULD use one of the locales in the array, with
preference to the first item in the array supported by the AS. If
none of the given locales are supported, the AS MAY use a default
locale.

2.5.6. Extending Interaction Modes

Additional interaction modes are defined in a registry TBD
(Section 12).

[[ See issue #61 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/61) ]]

2.6. Declaring RC Client Capabilities

If the RC client software supports extension capabilities, it the client
instance MAY present them to the AS in the "capabilities" field.
This field is an array of strings representing specific extensions
and capabilities, as defined by a registry TBD (Section 12).

"capabilities": ["ext1", "ext2"]

2.7. Referencing an Existing Grant Request

If the RC client instance has a reference handle from a previously
granted request, it MAY send that reference in the "existing_grant"
field. This field is a single string consisting of the "value" of
the "access_token" returned in a previous request's continuation
response (Section 3.1).

"existing_grant": "80UPRY5NM33OMUKMKSKU"

The AS MUST dereference the grant associated with the reference and
process this request in the context of the referenced one. The AS
MUST NOT alter the existing grant associated with the reference.

[[ See issue #62 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/62) ]]

2.8. Requesting OpenID Connect Claims

If the RC and AS both support OpenID Connect's claims query language
as defined in [OIDC] Section 5.5, the RC sends the value of the
OpenID Connect "claims" authorization request parameter as a JSON
object under the name "claims" in the root of the request.

"claims": {
"id_token" : {
"email" : { "essential" : true },
"email_verified" : { "essential" : true }
},
"userinfo" : {
"name" : { "essential" : true },
"picture" : null
}
}

The contents of the "claims" parameter have the same semantics as
they do in OpenID Connect's "claims" authorization request parameter,
including all extensions such as [OIDC4IA].

"existing_grant": "80UPRY5NM33OMUKMKSKU"

The AS MUST process the
claims object in dereference the same way that it would grant associated with an OAuth 2 based
authorization request.

Note that because this is an independent query object, the "claims"
value can augment or alter other portions of the request, namely the
"resources" reference and "subject" fields. This query language uses the
fields
process this request in the top level context of the object to indicate the target for any
requested claims. For instance, referenced one. The AS
MUST NOT alter the "userinfo" target indicates that
a returned access token would existing grant access to the given claims at the
UserInfo Endpoint, while the "id_token" target indicates that associated with the
claims would be returned in an ID Token as described in Section 3.4.

[[ See issue #63 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/63) ]] reference.

[[ See issue #64 #62 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/64)
issues/62) ]]

2.9.

2.8. Extending The Grant Request

The request object MAY be extended by registering new items in a
registry TBD (Section 12). Extensions SHOULD be orthogonal to other
parameters. Extensions MUST document any aspects where the extension
item affects or influences the values or behavior of other request
and response objects.

[[ See issue #65 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/65) ]]

3. Grant Response

In response to a RC's client instance's request, the AS responds with a
JSON object as the HTTP entity body. Each possible field is detailed
in the sections below

continue (object) Indicates that the RC client instance can continue
the request by making an additional request using these parameters. one or more continuation requests.
Section 3.1

access_token (object) A single access token that the RC client instance
can use to call the RS on behalf of the RO. Section 3.2.1

multiple_access_token (object) Multiple named access tokens that the
RC
client instance can use to call the RS on behalf of the RO.
Section 3.2.2

interact (object) Indicates that interaction through some set of
defined mechanisms needs to take place. Section 3.3

subject (object) Claims about the RO as known and declared by the
AS. Section 3.4

instance_id (string) An identifier this RC client instance instance can
use to identify itself when making future requests. Section 3.5

user_handle (string) An identifier this RC client instance instance can
use to identify its current RQ when making future requests.
Section 3.5

error (object) An error code indicating that something has gone
wrong. Section 3.6

In this example, the AS is returning an interaction URL
(Section 3.3.1), a callback nonce (Section 3.3.3), and a continuation
handle
response (Section 3.1).

{
"interact": {
"redirect": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
"callback": "MBDOFXG4Y5CVJCX821LH"
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/tx"
}
}

In this example, the AS is returning a bearer access token
(Section 3.2.1) with a management URL and a subject identifier
(Section 3.4) in the form of an email address.

3.1. Request Continuation

If the AS determines that the request can be continued with
additional requests, it responds with the "continue" field. This
field contains a JSON object with the following properties.

uri (string) REQUIRED. The URI at which the RC client instance can
make continuation requests. This URI MAY vary per request, or MAY
be stable at the AS if the AS includes an access token. The RC
client instance MUST use this value exactly as given when making a
continuation request (Section 5).

wait (integer) RECOMMENDED. The amount of time in integer seconds
the RC client instance SHOULD wait after receiving this continuation
handle and calling the URI.

access_token (object) RECOMMENDED. REQUIRED. A unique access token for
continuing the request, in the format specified in Section 3.2.1.
This access token MUST be bound to the RC's client instance's key used
in the request and MUST NOT be a "bearer" token. As a
consequence, the "key" field of this access token is always the
boolean value "true". This access token MUST NOT be usable at
resources outside of the AS. If the AS includes
an access token, the RC The client instance MUST present the
access token in all requests to the continuation URI as described
in Section 7. [[ See issue #66 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/66) (https://github.com/ietf-wg-gnap/
gnap-core-protocol/issues/66) ]]

{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}

The RC client instance can use the values of this field to continue the
request as described in Section 5. Note that the RC client instance
MUST sign all continuation requests with its key as described in
Section 8. If the AS includes
an "access_token", the RC 8 and MUST present the access token in its continuation
request.

This field SHOULD be returned when interaction is expected, to allow
the RC client instance to follow up after interaction has been
concluded.

[[ See issue #67 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/67) ]]

3.2. Access Tokens

If the AS has successfully granted one or more access tokens to the
RC,
client instance, the AS responds with either the "access_token" or
the "multiple_access_token" field. The AS MUST NOT respond with both
the "access_token" and "multiple_access_token" fields.

[[ See issue #68 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/68) ]]

3.2.1. Single Access Token

If the RC client instance has requested a single access token and the AS
has granted that access token, the AS responds with the
"access_token" field. The value of this field is an object with the
following properties.

value (string) REQUIRED. The value of the access token as a string.
The value is opaque to the RC. client instance. The value SHOULD be
limited to ASCII characters to facilitate transmission over HTTP
headers within other protocols without requiring additional
encoding.

manage (string) OPTIONAL. The management URI for this access token.

If provided, the RC client instance MAY manage its access token as
described in Section 6. This management URI is a function of the
AS and is separate from the RS the RC client instance is requesting
access to. This URI MUST NOT include the access token value and
SHOULD be different for each access token issued in a request.

resources (array of objects/strings) RECOMMENDED. A description of
the rights associated with this access token, as defined in
Section 2.1.1. If included, this MUST reflect the rights
associated with the issued access token. These rights MAY vary
from what was requested by the RC. client instance.

expires_in (integer) OPTIONAL. The number of seconds in which the
access will expire. The RC client instance MUST NOT use the access
token past this time. An RS MUST NOT accept an access token past
this time. Note that the access token MAY be revoked by the AS or
RS at any point prior to its expiration.

key (object / string / boolean) REQUIRED. The key that the token is
bound to. If the boolean value "true" is used, the token is bound
to the key used by the RC client instance (Section 2.3.2) in its
request for access. If the boolean value "false" is used, the
token is a bearer token with no key bound to it. Otherwise, the
key MUST be an object or string in a format described in
Section 2.3.2, describing a public key to which the RC client
instance can use the associated private key. The RC client instance
MUST be able to dereference or process the key information in
order to be able to sign the request.

The following non-normative example shows a single bearer token with
a management URL that has access to three described resources.

"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"key": false,
"manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata"
]
}

The following non-normative example shows a single access token bound
to the RC's client instance's key, which was presented using the detached
JWS (Section 8.1) binding method.

"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"key": true,
"resources": [
"finance", "medical"
]
}

If the RC client instance requested multiple access tokens
(Section 2.1.3), the AS MUST NOT respond with a single access token
structure unless the RC client instance sends the "split_token" flag as
described in Section 2.1.4.

[[ See issue #69 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/69) ]]

3.2.2. Multiple Access Tokens

If the RC client instance has requested multiple access tokens and the
AS has granted at least one of them, the AS responds with the
"multiple_access_tokens" field. The value of this field is a JSON
object, and the property names correspond to the token identifiers
chosen by the RC client instance in the multiple access token request
(Section 2.1.3). The values of the properties of this object are
access tokens as described in Section 3.2.1.

In this non-normative example, two bearer tokens are issued under the
names "token1" and "token2", and only the first token has a
management URL associated with it.

"multiple_access_tokens": {
"token1": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"key": false,
"manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
},
"token2": {
"value": "UFGLO2FDAFG7VGZZPJ3IZEMN21EVU71FHCARP4J1",
"key": false
}
}

Each access token corresponds to the named resources arrays in the
RC's
client instance's request (Section 2.1.3).

The multiple access token response MUST be used when multiple access
tokens are requested, even if only one access token is issued as a
result of the request. The AS MAY refuse to issue one or more of the
requested access tokens, for any reason. In such cases the refused
token is omitted from the response and all of the other issued access
tokens are included in the response the requested names appropriate
names.

If the RC client instance requested a single access token
(Section 2.1.1), the AS MUST NOT respond with the multiple access
token structure unless the
RC client instance sends the "split_token"
flag as described in Section 2.1.4.

Each access token MAY have different proofing mechanisms. If
management is allowed, each access token SHOULD have different
management URIs.

[[ See issue #70 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/70) ]]

3.3. Interaction Modes

If the RC client instance has indicated a capability to interact with
the RO in its request (Section 2.5), and the AS has determined that
interaction is both supported and necessary, the AS responds to the RC
client instance with any of the following values in the "interact"
field of the response. There is no preference order for interaction
modes in the response, and it is up to the RC client instance to
determine which ones to use. All supported interaction methods are
included in the same "interact" object.

redirect (string) Redirect to an arbitrary URL. Section 3.3.1

app (string) Launch of an application URL. Section 3.3.2

callback (string) Callback to an RC a client instance accessible URL after
interaction is completed. Section 3.3.3

user_code (object) Display a short user code. Section 3.3.4

Additional interaction mode responses can be defined in a registry
TBD (Section 12).

The AS MUST NOT respond with any interaction mode that the RC client
instance did not indicate in its request. The AS MUST NOT respond
with any interaction mode that the AS does not support. Since
interaction responses include secret or unique information, the AS
SHOULD respond to each interaction mode only once in an ongoing
request, particularly if the RC client instance modifies its request
(Section 5.3).

3.3.1. Redirection to an arbitrary URL

If the RC client instance indicates that it can redirect to an arbitrary
URL (Section 2.5.1) and the AS supports this mode for the RC's client
instance's request, the AS responds with the "redirect" field, which
is a string containing the URL to direct the RQ to. This URL MUST be
unique for the request and MUST NOT contain any security-sensitive
information.

"interact": {
"redirect": "https://interact.example.com/4CF492MLVMSW9MKMXKHQ"
}

The interaction URL returned represents a function of the AS but MAY
be completely distinct from the URL the RC client instance uses to
request access (Section 2), allowing an AS to separate its user-interactive user-
interactive functionality from its back-end security functionality.

[[ See issue #72 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/72) ]]

The RC client instance sends the RQ to the URL to interact with the AS.
The RC client instance MUST NOT alter the URL in any way. The means for
the RC client instance to send the RQ to this URL is out of scope of
this specification, but common methods include an HTTP redirect,
launching the system browser, displaying a scannable code, or
printing out the URL in an interactive console.

3.3.2. Launch of an application URL

If the RC client instance indicates that it can launch an application
URL (Section 2.5.2) and the AS supports this mode for the RC's client
instance's request, the AS responds with the "app" field, which is a
string containing the URL to direct the RQ to. This URL MUST be
unique for the request and MUST NOT contain any security-sensitive
information.

"interact": {
"app": "https://app.example.com/launch?tx=4CF492MLV"
}

The RC client instance launches the URL as appropriate on its platform,
and the means for the RC client instance to launch this URL is out of
scope of this specification. The RC client instance MUST NOT alter the
URL in any way. The RC client instance MAY attempt to detect if an
installed application will service the URL being sent before
attempting to launch the application URL.

[[ See issue #71 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/71) ]]

3.3.3. Post-interaction Callback to an RC a Client Instance Accessible URL

If the RC client instance indicates that it can receive a
post-interaction callback on a URL (Section 2.5.3) and the AS
supports this mode for the RC's client instance's request, the AS responds
with a "callback" field containing a nonce that the RC client instance
will use in validating the callback as defined in Section 4.4.1.

"interact": {
"callback": "MBDOFXG4Y5CVJCX821LH"
}

[[ See issue #73 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/73) ]]

When the RO completes interaction at the AS, the AS MUST call the
RC's
client instance's callback URL using the method indicated in the
callback request (Section 2.5.3) as described in Section 4.4.1.

If the AS returns a "callback" nonce, the RC client instance MUST NOT
continue a grant request before it receives the associated
interaction reference on the callback URI.

3.3.4. Display of a Short User Code

If the RC client instance indicates that it can display a short
user-typeable code (Section 2.5.4) and the AS supports this mode for
the RC's client instance's request, the AS responds with a "user_code"
field. This field is an object that contains the following members.

code (string) REQUIRED. A unique short code that the user can type
into an authorization server. This string MUST be case-
insensitive, MUST consist of only easily typeable characters (such
as letters or numbers). The time in which this code will be
accepted SHOULD be short lived, such as several minutes. It is
RECOMMENDED that this code be no more than eight characters in
length.

url (string) RECOMMENDED. The interaction URL that the RC client
instance will direct the RO to. This URL MUST be stable at the AS
such that RCs client instance's can be statically configured with it.

"interact": {
"user_code": {
"code": "A1BC-3DFF",
"url": "https://srv.ex/device"
}
}

The RC client instance MUST communicate the "code" to the RQ in some
fashion, such as displaying it on a screen or reading it out audibly.
The "code" is a one-time-use credential that the AS uses to identify
the pending request from the RC. client instance. When the RO enters
this code (Section 4.2) into the AS, the AS MUST determine the
pending request that it was associated with. If the AS does not
recognize the entered code, the AS MUST display an error to the user.
If the AS detects too many unrecognized codes entered, it SHOULD
display an error to the user.

The RC client instance SHOULD also communicate the URL if possible to
facilitate user interaction, but since the URL should be stable, the RC
client instance should be able to safely decide to not display this
value. As this interaction mode is designed to facilitate
interaction via a secondary device, it is not expected that the RC
client instance redirect the RQ to the URL given here at runtime.
Consequently, the URL needs to be stable enough that a RC client
instance could be statically configured with it, perhaps referring
the RQ to the URL via documentation instead of through an interactive
means. If the RC client instance is capable of communicating an
arbitrary URL to the RQ, such as through a scannable code, the RC client
instance can use the "redirect" (Section 2.5.1) mode for this purpose
instead of or in addition to the user code mode.

[[ See issue #72 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/72) ]]

3.3.5. Extending Interaction Mode Responses

Extensions to this specification can define new interaction mode
responses in a registry TBD (Section 12). Extensions MUST document
the corresponding interaction request.

3.4. Returning User Information

If information about the RO is requested and the AS grants the RC client
instance access to that data, the AS returns the approved information
in the "subject" response field. This field is an object with the
following OPTIONAL properties.

sub_ids (array of strings) objects) An array of subject identifiers for the
RO, as defined by [I-D.ietf-secevent-subject-identifiers]. [[ See
issue #74 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/74) ]]

assertions (object) An object containing assertions as values keyed
on the assertion type defined by a registry TBD (Section 12). [[
See issue #41 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/41) ]]

updated_at (string) Timestamp as an ISO8610 date string, indicating
when the identified account was last updated. The RC client instance
MAY use this value to determine if it needs to request updated
profile information through an identity API. The definition of
such an identity API is out of scope for this specification.

"subject": {
"sub_ids": [ {
"subject_type": "email",
"email": "user@example.com",
} ],
"assertions": {
"id_token": "eyj..."
}
}

The AS MUST return the "subject" field only in cases where the AS is
sure that the RO and the RQ are the same party. This can be
accomplished through some forms of interaction with the RO
(Section 4).

Subject identifiers returned by the AS SHOULD uniquely identify the
RO at the AS. Some forms of subject identifier are opaque to the RC
client instance (such as the subject of an issuer and subject pair),
while others forms (such as email address and phone number) are
intended to allow the RC client instance to correlate the identifier
with other account information at the RC. client instance. The RC client
instance MUST NOT request or use any returned subject identifiers for
communication purposes (see Section 2.2). That is, a subject
identifier returned in the format of an email address or a phone
number only identifies the RO to the AS and does not indicate that
the AS has validated that the represented email address or phone
number in the identifier is suitable for communication with the
current user. To get such information, the RC client instance MUST use
an identity protocol to request and receive additional identity
claims. While
Section 2.8 specifies one such method, other identity protocols could
also be used on top of GNAP to convey this information and the The details of an identity protocol and associated schema
are outside the scope of this specification.

[[ See issue #75 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/75) ]]

[[ See issue #74 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/74) ]]

Extensions to this specification MAY define additional response
properties in a registry TBD (Section 12).

3.5. Returning Dynamically-bound Reference Handles

Many parts of the RC's client instance's request can be passed as either a
value or a reference. The use of a reference in place of a value
allows for a client instance to optimize requests to the AS.

Some references, such as for the RC client instance's identity
(Section 2.3.1) or the requested resources (Section 2.1.2), can be
managed statically through an admin console or developer portal
provided by the AS or RS. The developer of the RC client software can
include these values in their code for a more efficient and compact
request.

If desired, the AS MAY also generate and return some of these
references dynamically to the RC client instance in its response to
facilitate multiple interactions with the same software. The RC client
instance SHOULD use these references in future requests in lieu of
sending the associated data value. These handles are intended to be
used on future requests.

Dynamically generated handles are string values that MUST be
protected by the RC client instance as secrets. Handle values MUST be
unguessable and MUST NOT contain any sensitive information. Handle
values are opaque to the RC.

[[ See issue #76 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/76) ]] client instance.

All dynamically generated handles are returned as fields in the root
JSON object of the response. This specification defines the
following dynamic handle returns, additional handles can be defined
in a registry TBD (Section 12).

instance_id (string) A string value used to represent the
information in the "client" object that the RC client instance can
use in a future request, as described in Section 2.3.1.

user_handle (string) A string value used to represent the current
user. The RC client instance can use in a future request, as
described in Section 2.4.1.

This non-normative example shows two handles along side an issued
access token.

{
"user_handle": "XUT2MFM1XBIKJKSDU8QM",
"instance_id": "7C7C4AZ9KHRS6X63AJAO",
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"key": false
}
}

[[ See issue #77 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/77) ]]

[[ See issue #78 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/78) ]]

3.6. Error Response

If the AS determines that the request cannot be issued for any
reason, it responds to the RC client instance with an error message.

error (string) The error code.

{

"error": "user_denied"

}

The error code is one of the following, with additional values
available in a registry TBD (Section 12):

user_denied The RO denied the request.

too_fast The RC client instance did not respect the timeout in the wait
response.

unknown_request The request referenced an unknown ongoing access
request.

[[ See issue #79 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/79) ]]

3.7. Extending the Response

Extensions to this specification MAY define additional fields for the
grant response in a registry TBD (Section 12).

[[ See issue #80 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/80) ]]

4. Interaction at the AS

If the RC client instance indicates that it is capable of driving
interaction with the RO in its request (Section 2.5), and the AS
determines that interaction is required and responds to one or more
of the RC's client instance's interaction modes, the RC client instance
SHOULD initiate one of the returned interaction modes in the response
(Section 3.3).

When the RO is interacting with the AS, the AS MAY perform whatever
actions it sees fit, including but not limited to:

* authenticate the current user (who may be the RQ) as the RO
* gather consent and authorization from the RO for access to
requested resources and direct information

* allow the RO to modify the parameters of the request (such as
disallowing some requested resources or specifying an account or
record)

* provide warnings to the RO about potential attacks or negative
effects of the requested information

[[ See issue #81 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/81) ]]

4.1. Interaction at a Redirected URI

When the RO is directed to the AS through the "redirect"
(Section 3.3.1) mode, the AS can interact with the RO through their
web browser to authenticate the user as an RO and gather their
consent. Note that since the RC client instance does not add any
parameters to the URL, the AS MUST determine the grant request being
referenced from the URL value itself. If the URL cannot be
associated with a currently active request, the AS MUST display an
error to the RO and MUST NOT attempt to redirect the RO back to any RC
client instance even if a callback is supplied (Section 2.5.3).

The interaction URL MUST be reachable from the RO's browser, though
note that the RO MAY open the URL on a separate device from the RC
client instance itself. The interaction URL MUST be accessible from
an HTTP GET request, and MUST be protected by HTTPS or equivalent
means.

With this method, it is common for the RO to be the same party as the
RQ, since the RC client instance has to communicate the redirection URI
to the RQ.

4.2. Interaction at the User Code URI

When the RO is directed to the AS through the "user_code"
(Section 3.3.4) mode, the AS can interact with the RO through their
web browser to collect the user code, authenticate the user as an RO,
and gather their consent. Note that since the URL itself is static,
the AS MUST determine the grant request being referenced from the
user code value itself. If the user code cannot be associated with a
currently active request, the AS MUST display an error to the RO and
MUST NOT attempt to redirect the RO back to any RC client instance even
if a callback is supplied (Section 2.5.3).

The user code URL MUST be reachable from the RO's browser, though
note that the RO MAY open the URL on a separate device from the RC
client instance itself. The user code URL MUST be accessible from an
HTTP GET request, and MUST be protected by HTTPS or equivalent means.

While it is common for the RO to be the same party as the RQ, since
the RC client instance has to communicate the user code to someone,
there are cases where the RQ and RO are separate parties and the
authorization happens asynchronously.

4.3. Interaction through an Application URI

When the RC client instance successfully launches an application through
the "app" mode (Section 3.3.2), the AS interacts with the RO through
that application to authenticate the user as the RO and gather their
consent. The details of this interaction are out of scope for this
specification.

[[ See issue #82 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/82) ]]

4.4. Post-Interaction Completion

Upon completing an interaction with the RO, if a "callback"
(Section 3.3.3) mode is available with the current request, the AS
MUST follow the appropriate method at the end of interaction to allow
the RC client instance to continue. If this mode is not available, the
AS SHOULD instruct the RO to return to their RC software client instance upon
completion. Note that these steps still take place in most error
cases, such as when the RO has denied access. This pattern allows
the RC client instance to potentially recover from the error state
without restarting the request from scratch by modifying its request
or providing additional information directly to the AS.

[[ See issue #83 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/83) ]]

The AS MUST create an interaction reference and associate that
reference with the current interaction and the underlying pending
request. This value MUST be sufficiently random so as not to be
guessable by an attacker. The interaction reference MUST be one-
time-use.

The AS MUST calculate a hash value based on the RC client instance and
AS nonces and the interaction reference, as described in
Section 4.4.3. The RC client instance will use this value to validate
the return call from the AS.

The AS then MUST send the hash and interaction reference based on the
interaction finalization mode as described in the following sections.

4.4.1. Completing Interaction with a Browser Redirect to the Callback
URI

When using the "callback" interaction mode (Section 3.3.3) with the
"redirect" method, the AS signals to the RC client instance that
interaction is complete and the request can be continued by directing
the RO (in their browser) back to the RC's client instance's callback URL
sent in the callback request (Section 2.5.3.1).

The AS secures this callback by adding the hash and interaction
reference as query parameters to the RC's client instance's callback URL.

hash REQUIRED. The interaction hash value as described in
Section 4.4.3.

interact_ref REQUIRED. The interaction reference generated for this
interaction.

The means of directing the RO to this URL are outside the scope of
this specification, but common options include redirecting the RO
from a web page and launching the system browser with the target URL.

https://client.example.net/return/123455
?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
&interact_ref=4IFWWIKYBC2PQ6U56NL1

When receiving the request, the RC client instance MUST parse the query
parameters to calculate and validate the hash value as described in
Section 4.4.3. If the hash validates, the RC client instance sends a
continuation request to the AS as described in Section 5.1 using the
interaction reference value received here.

4.4.2. Completing Interaction with a Direct HTTP Request Callback

When using the "callback" interaction mode (Section 3.3.3) with the
"push" method, the AS signals to the RC client instance that interaction
is complete and the request can be continued by sending an HTTP POST
request to the RC's client instance's callback URL sent in the callback
request (Section 2.5.3.2).

The entity message body is a JSON object consisting of the following
two fields:

hash (string) REQUIRED. The interaction hash value as described in
Section 4.4.3.

interact_ref (string) REQUIRED. The interaction reference generated
for this interaction.

POST /push/554321 HTTP/1.1
Host: client.example.net
Content-Type: application/json

{
"hash": "p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A",
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
When receiving the request, the RC client instance MUST parse the JSON
object and validate the hash value as described in Section 4.4.3. If
the hash validates, the RC client instance sends a continuation request
to the AS as described in Section 5.1 using the interaction reference
value received here.

4.4.3. Calculating the interaction hash

The "hash" parameter in the request to the RC's client instance's callback
URL ties the front channel response to an ongoing request by using
values known only to the parties involved. This security mechanism
allows the RC client instance to protect itself against several kinds of
session fixation and injection attacks. The AS MUST always provide
this hash, and the RC client instance MUST validate the hash when
received.

[[ See issue #84 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/84) ]]

To calculate the "hash" value, the party doing the calculation first
takes the "nonce" value sent by the RC client instance in the
interaction section of the initial request (Section 2.5.3), the AS's
nonce value from the callback response (Section 3.3.3), and the
"interact_ref" sent to the
RC's client instance's callback URL. These
three values are concatenated to each other in this order using a
single newline character as a separator between the fields. There is
no padding or whitespace before or after any of the lines, and no
trailing newline character.

VJLO6A4CAYLBXHTR0KRO
MBDOFXG4Y5CVJCX821LH
4IFWWIKYBC2PQ6U56NL1

The party then hashes this string with the appropriate algorithm
based on the "hash_method" parameter of the "callback". If the
"hash_method" value is not present in the RC's client instance's request,
the algorithm defaults to "sha3".

[[ See issue #56 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/56) ]]

4.4.3.1. SHA3-512

The "sha3" hash method consists of hashing the input string with the
512-bit SHA3 algorithm. The byte array is then encoded using URL
Safe Base64 with no padding. The resulting string is the hash value.

p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
4.4.3.2. SHA2-512

The "sha2" hash method consists of hashing the input string with the
512-bit SHA2 algorithm. The byte array is then encoded using URL
Safe Base64 with no padding. The resulting string is the hash value.

62SbcD3Xs7L40rjgALA-ymQujoh2LB2hPJyX9vlcr1H6ecChZ8BNKkG_HrOKP_Bpj84rh4mC9aE9x7HPBFcIHw

5. Continuing a Grant Request

While it is possible for the AS to return a Section 3 with all the
RC's
client instance's requested information (including access tokens
(Section 3.2) and direct user information (Section 3.4)), it's more
common that the AS and the RC client instance will need to communicate
several times over the lifetime of an access grant. This is often
part of facilitating interaction (Section 4), but it could also be
used to allow the AS and RC client instance to continue negotiating the
parameters of the original grant request (Section 2).

To enable this ongoing negotiation, the AS provides a continuation
API to the client software. The AS returns a "continue" field in the
response (Section 3.1) that contains information the RC client instance
needs to continue access this process with another request, API, including a URI to access as well as an optional
access token to use during the continued requests.

When

The access token is initially bound to the RC same key and method the
client instance used to make the initial request. As a consequence,
when the client instance makes any calls to the continuation URL, the RC
client instance MUST present the access token as described in
Section 7 and present proof of the client instance's key (or its most
recent key associated with this ongoing
request rotation) by signing the request as described in Section 8. The key in
use will be either the key from the initial request (Section 2.3.2)
or its most recent rotation.

[[ See issue #85 (https://github.com/
ietf-wg-gnap/gnap-core-protocol/issues/85) (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/85) ]]

For example, here the RC client instance makes a POST request and signs with detached
JWS:

POST /continue/80UPRY5NM33OMUKMKSKU HTTP/1.1
Host: server.example.com
Detached-JWS: ejy0...

If the AS includes an "access_token" in the "continue" response in
Section 3.1, the RC MUST include the access token the request as
described in Section 7. Note that the access token is always bound to the RC's presented key (or its most recent rotation).

For example, here the RC makes a POST request with the interaction
reference, includes the access token,
unique URI and signs the request with detached JWS:

POST /continue /continue/KSKUOMUKM HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Host: server.example.com
Detached-JWS: ejy0...

{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}

The AS MUST be able to tell from the RC's client instance's request which
specific ongoing request is being accessed. Common methods for doing so
include accessed, using a unique, unguessable URL for each continuation
response, associating combination of
the request with continuation URL, the provided access token, or
allowing only a single ongoing grant request for a given RC and the client
instance
at a time. identified by the key signature. If the AS cannot determine
a single active grant request to map the continuation request to, the
AS MUST return an error.

The ability to continue an already-started request allows the RC client
instance to perform several important functions, including presenting
additional information from interaction, modifying the initial
request, and getting the current state of the request.

All requests to the continuation API are protected by this bound
access token. For example, here the client instance makes a POST
request to a stable continuation endpoint URL with the interaction
reference (Section 5.1), includes the access token, and signs with
detached JWS:

POST /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}

If a "wait" parameter was included in the continuation response
(Section 3.1), the RC client instance MUST NOT call the continuation URI
prior to waiting the number of seconds indicated. If no "wait"
period is indicated, the RC client instance SHOULD wait at least 5 seconds
seconds. If the RC client instance does not respect the given wait
period, the AS MUST return an error. [[ See issue #86 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/86)
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/86) ]]

The response from the AS is a JSON object and MAY contain any of the
fields described in Section 3, as described in more detail in the
sections below.

If the AS determines that the RC client instance can make a further
continuation request, the AS MUST include a new "continue" response
(Section 3.1).
If the continuation was previously bound to an access token, the The new "continue" response MUST include a bound
access token as well, and this token SHOULD be a new access token,
invalidating the previous access token. If the AS does not return a
new "continue" response, the RC client instance MUST NOT make an
additional continuation request. If a RC client instance does so, the
AS MUST return an error. [[ See issue #87 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/87) (https://github.com/ietf-
wg-gnap/gnap-core-protocol/issues/87) ]]

For continuation functions that require the RC client instance to send a
message body, the body MUST be a JSON object.

5.1. Continuing After a Completed Interaction

When the AS responds to the RC's client instance's "callback" parameter as
in Section 4.4.1, this response includes an interaction reference.
The
RC client instance MUST include that value as the field
"interact_ref" in a POST request to the continuation URI.

POST /continue/80UPRY5NM33OMUKMKSKU /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}

Since the interaction reference is a one-time-use value as described
in Section 4.4.1, if the RC client instance needs to make additional
continuation calls after this request, the RC client instance MUST NOT
include the interaction reference. If the AS detects an RC a client
instance submitting the same interaction reference multiple times,
the AS MUST return an error and SHOULD invalidate the ongoing
request.

The Section 3 MAY contain any newly-created access tokens
(Section 3.2) or newly-released subject claims (Section 3.4). The
response MAY contain a new "continue" response (Section 3.1) as
described above. The response SHOULD NOT contain any interaction
responses (Section 3.3). [[ See issue #89 (https://github.com/ietf-
wg-gnap/gnap-core-protocol/issues/89) ]]

For example, if the request is successful in causing the AS to issue
access tokens and release subject claims, the response could look
like this:

With this example, the RC client instance can not make an additional
continuation request because a "continue" field is not included.

[[ See issue #88 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/88) ]]

5.2. Continuing During Pending Interaction

When the RC client instance does not include a "callback" parameter, the RC
client instance will often need to poll the AS until the RO has
authorized the request. To do so, the RC client instance makes a POST
request to the continuation URI as in Section 5.1, but does not
include a message body.

POST /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

The Section 3 MAY contain any newly-created access tokens
(Section 3.2) or newly-released subject claims (Section 3.4). The
response MAY contain a new "continue" response (Section 3.1) as
described above. If a "continue" field is included, it SHOULD
include a "wait" field to facilitate a reasonable polling rate by the
RC.
client instance. The response SHOULD NOT contain interaction
responses (Section 3.3).

For example, if the request has not yet been authorized by the RO,
the AS could respond by telling the RC client instance to make another
continuation request in the future. In this example, a new, unique
access token has been issued for the call, which the RC client instance
will use in its next continuation request.

{
"continue": {
"access_token": {
"value": "33OMUKMKSKU80UPRY5NM",
"key": true
},
"uri": "https://server.example.com/continue",
"wait": 30
}
}

[[ See issue #90 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/90) ]]

[[ See issue #91 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/91) ]]

If the request is successful in causing the AS to issue access tokens
and release subject claims, the response could look like this
example:

5.3. Modifying an Existing Request

The RC client instance might need to modify an ongoing request, whether
or not tokens have already been issued or claims have already been
released. In such cases, the RC client instance makes an HTTP PATCH
request to the continuation URI and includes any fields it needs to
modify. Fields that aren't included in the request are considered
unchanged from the original request.

The RC client instance MAY include the "resources" and "subject" fields
as described in Section 2.1 and Section 2.2. Inclusion of these
fields override any values in the initial request, which MAY trigger
additional requirements and policies by the AS. For example, if the RC
client instance is asking for more access, the AS could require
additional interaction with the RO to gather additional consent. If
the RC client instance is asking for more limited access, the AS could
determine that sufficient authorization has been granted to the RC
client instance and return the more limited access rights
immediately. [[ See issue #92 (https://github.com/
ietf-wg-gnap/gnap-core-protocol/issues/92) (https://github.com/ietf-wg-gnap/gnap-
core-protocol/issues/92) ]]

The RC client instance MAY include the "interact" field as described in
Section 2.5. Inclusion of this field indicates that the RC client
instance is capable of driving interaction with the RO, and this
field replaces any values from a previous request. The AS MAY
respond to any of the interaction responses as described in
Section 3.3, just like it would to a new request.

The RC client instance MAY include the "user" field as described in
Section 2.4 to present new assertions or information about the RQ.
[[ See issue #93
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/93) (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/93) ]]

The RC client instance MUST NOT include the "client" section of the
request. [[ See issue #94 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/94) (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/94) ]]

The RC client instance MAY include post-interaction responses such as
described in Section 5.1. [[ See issue #95 (https://github.com/ietf-wg-gnap/gnap-
core-protocol/issues/95) (https://github.com/ietf-
wg-gnap/gnap-core-protocol/issues/95) ]]

Modification requests MUST NOT alter previously-issued access tokens.
Instead, any access tokens issued from a continuation are considered
new, separate access tokens. The AS MAY revoke existing access
tokens after a modification has occurred. [[ See issue #96
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/96) ]]

If the modified request can be granted immediately by the AS, the
Section 3 MAY contain any newly-created access tokens (Section 3.2)
or newly-released subject claims (Section 3.4). The response MAY
contain a new "continue" response (Section 3.1) as described above.
If interaction can occur, the response SHOULD contain interaction
responses (Section 3.3) as well.

For example, an RC a client instance initially requests a set of resources
using references:

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
"read", "write"
],
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"client": "987YHGRT56789IOLK"
}

Access is granted by the RO, and a token is issued by the AS. In its
final response, the AS includes a "continue" field: field, which includes a
separate access token for accessing the continuation API:

{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": ... {
"value": "RP1LT0-OS9M2P_R64TB",
"key": false,
"resources": [
"read", "write"
]
}
}

This "continue" field allows the RC client instance to make an eventual
continuation call. The RC In the future, the client instance realizes that
it no longer needs "write" access and therefore modifies its ongoing
request, here asking for just "read" access instead of both "read"
and "write" as before.

PATCH /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

{
"resources": [
"read"
]
...
}

The AS replaces the previous "resources" from the first request,
allowing the AS to determine if any previously-granted consent
already applies. In this case, the AS would likely determine that
reducing the breadth of the requested access means that new access
tokens can be issued to the RC. client instance. The AS would likely
revoke previously-issued access tokens that had the greater access
rights associated with them.

{
"continue": {
"access_token": {
"value": "M33OMUK80UPRY5NMKSKU",
"key": true
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": ... {
"value": "0EVKC7-2ZKwZM_6N760",
"key": false,
"resources": [
"read"
]
}
}

For another example, the RC client instance initially requests read-only
access but later needs to step up its access. The initial request
could look like this example.

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
"read"
],
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"client": "987YHGRT56789IOLK"
}

Access is granted by the RO, and a token is issued by the AS. In its
final response, the AS includes a "continue" field:

This allows the RC client instance to make an eventual continuation
call. The RC client instance later realizes that it now needs "write"
access in addition to the "read" access. Since this is an expansion
of what it asked for previously, the RC client instance also includes a
new interaction section in case the AS needs to interact with the RO
again to gather additional authorization. Note that the RC's client
instance's nonce and callback are different from the initial request.

Since the original callback was already used in the initial exchange,
and the callback is intended for one-
time-use, one-time-use, a new one needs to be
included in order to use the callback again.

[[ See issue #97 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/97) ]]

PATCH /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

{
"resources": [
"read", "write"
],
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/654321",
"nonce": "K82FX4T4LKLTI25DQFZC"
}
}
}

From here, the AS can determine that the RC client instance is asking
for more than it was previously granted, but since the RC client
instance has also provided a mechanism to interact with the RO, the
AS can use that to gather the additional consent. The protocol
continues as it would with a new request. Since the old access
tokens are good for a subset of the rights requested here, the AS
might decide to not revoke them. However, any access tokens granted
after this update process are new access tokens and do not modify the
rights of existing access tokens.

5.4. Getting the Current State of a Grant Request

If the RC client instance needs to get the current state of an ongoing
grant request, it makes an HTTP GET request to the continuation URI.
This request MUST NOT alter the grant request in any fashion,
including causing the issuance of new access tokens or modification
of interaction parameters.

The AS MAY include existing access tokens and previously-released
subject claims in the response. The AS MUST NOT issue a new access
token or release a new subject claim in response to this request.

GET /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

The response MAY include any fields described Section 3 that are
applicable to this ongoing request, including the most recently
issued access tokens, any released subject claims, and any currently
active interaction modes. The response MAY contain a new "continue"
response (Section 3.1) as described above.

[[ See issue #98 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/98) ]]

5.5. Canceling a Grant Request

If the RC client instance wishes to cancel an ongoing grant request, it
makes an HTTP DELETE request to the continuation URI.

DELETE /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

If the request is successfully cancelled, the AS responds with an
HTTP 202. The AS MUST revoke all associated access tokens, if
possible.

6. Token Management

If an access token response includes the "manage" parameter as
described in Section 3.2.1, the RC client instance MAY call this URL to
manage the access token with any of the actions defined in the
following sections. Other actions are undefined by this
specification.

The access token being managed acts as the access element for its own
management API. The RC client instance MUST present proof of an
appropriate key along with the access token.

If the token is sender-constrained (i.e., not a bearer token), it
MUST be sent with the appropriate binding for the access token
(Section 7).

If the token is a bearer token, the RC client instance MUST present
proof of the same key identified in the initial request
(Section 2.3.2) as described in Section 8.

The AS MUST validate the proof and assure that it is associated with
either the token itself or the RC client instance the token was issued
to, as appropriate for the token's presentation type.

[[ See issue #99 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/99) ]]

6.1. Rotating the Access Token

The RC client instance makes an HTTP POST to the token management URI,
sending the access token in the appropriate header and signing the
request with the appropriate key.

POST /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
Host: server.example.com
Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
Detached-JWS: eyj0....

[[ See issue #100 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/100) ]]

The AS validates that the token presented is associated with the
management URL, that the AS issued the token to the given RC, client
instance, and that the presented key is appropriate to the token.

If the access token has expired, the AS SHOULD honor the rotation
request to the token management URL since it is likely that the RC
client instance is attempting to refresh the expired token. To
support this, the AS MAY apply different lifetimes for the use of the
token in management vs. its use at an RS. An AS MUST NOT honor a
rotation request for an access token that has been revoked, either by
the AS or by the RC client instance through the token management URI
(Section 6.2).

If the token is validated and the key is appropriate for the request,
the AS MUST invalidate the current access token associated with this
URL, if possible, and return a new access token response as described
in Section 3.2.1, unless the "multi_token" flag is specified in the
request. The value of the access token MUST NOT be the same as the
current value of the access token used to access the management API.
The response MAY include an updated access token management URL as
well, and if so, the RC client instance MUST use this new URL to manage
the new access token. [[ See issue #101 (https://github.com/ietf-wg-gnap/
gnap-core-protocol/issues/101) (https://github.com/ietf-wg-
gnap/gnap-core-protocol/issues/101) ]]

[[ See issue #102 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/102) ]]

{
"access_token": {
"value": "FP6A8H6HY37MH13CK76LBZ6Y1UADG6VEUPEER5H2",
"key": false,
"manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata"
]
}
}

[[ See issue #103 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/103) ]]

6.2. Revoking the Access Token

If the RC client instance wishes to revoke the access token proactively,
such as when a user indicates to the RC client instance that they no
longer wish for it to have access or the RC client instance application
detects that it is being uninstalled, the RC client instance can use the
token management URI to indicate to the AS that the AS should
invalidate the access token for all purposes.

The RC client instance makes an HTTP DELETE request to the token
management URI, presenting the access token and signing the request
with the appropriate key.

DELETE /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
Host: server.example.com
Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
Detached-JWS: eyj0....

If the key presented is associated with the token (or the RC, client
instance, in the case of a bearer token), the AS MUST invalidate the
access token, if possible, and return an HTTP 204 response code.

204 No Content

Though the AS MAY revoke an access token at any time for any reason,
the token management function is specifically for the RC's client
instance's use. If the access token has already expired or has been
revoked through other means, the AS SHOULD honor the revocation
request to the token management URL as valid, since the end result is
still the token not being usable.

7. Using Access Tokens

The method the RC client instance uses to send an access token to the RS
depends on the value of the "key" and "proof" parameters in the
access token response (Section 3.2.1).

If the key value is the boolean "false", the access token is a bearer
token sent using the HTTP Header method defined in [RFC6750].

Authorization: Bearer OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0

The form parameter and query parameter methods of [RFC6750] MUST NOT
be used.

If the "key" value is the boolean "true", the access token MUST be
sent to the RS using the same key and proofing mechanism that the RC
client instance used in its initial request.

If the "key" value is an object, the value of the "proof" field
within the key indicates the particular proofing mechanism to use.
The access token is sent using the HTTP authorization scheme "GNAP"
along with a key proof as described in Section 8 for the key bound to
the access token. For example, a "jwsd"-bound access token is sent
as follows:

Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
Detached-JWS: eyj0....

[[ See issue #104 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/104) ]]

8. Binding Keys

Any keys presented by the RC client instance to the AS or RS MUST be
validated as part of the request in which they are presented. The
type of binding used is indicated by the proof parameter of the key
section in the initial request Section 2.3.2. Values defined by this
specification are as follows:

jwsd A detached JWS signature header

jws Attached JWS payload

mtls Mutual TLS certificate verification

dpop OAuth Demonstration of Proof-of-Possession key proof header

httpsig HTTP Signing signature header

oauthpop OAuth PoP key proof authentication header

Additional proofing methods are defined by a registry TBD
(Section 12).

All key binding methods used by this specification MUST cover all
relevant portions of the request, including anything that would
change the nature of the request, to allow for secure validation of
the request by the AS. Relevant aspects include the URI being
called, the HTTP method being used, any relevant HTTP headers and
values, and the HTTP message body itself. The recipient of the
signed message MUST validate all components of the signed message to
ensure that nothing has been tampered with or substituted in a way
that would change the nature of the request.

When used for delegation in GNAP, these key binding mechanisms allow
the AS to ensure that the keys presented by the RC client instance in
the initial request are in control of the party calling any follow-up
or continuation requests. To facilitate this requirement, all keys in the initial request Section 2.3.2
continuation response (Section 3.1) includes an access token bound to
the client instance's key (Section 2.3.2), and that key (or its most
recent rotation) MUST be proved in all continuation requests
Section 5 and token 5. Token management requests Section 6, modulo
any rotations on those keys over time that 6 are similarly bound
to either the AS knows about. access token's own key or, in the case of bearer
tokens, the client instance's key. The AS MUST validate all keys
presented by the RC client instance (Section 2.3.2) or referenced in an
ongoing request for each call within that request.

[[ See issue #105 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/105) ]]
When used to bind to an access token, the access token MUST be
covered by the signature method.

8.1. Detached JWS

This method is indicated by "jwsd" in the "proof" field. A JWS
[RFC7515] signature object is created as follows:

The header of the JWS MUST contain the "kid" field of the key bound
to this RC client instance for this request. The JWS header MUST
contain an "alg" field appropriate for the key identified by kid and
MUST NOT be "none". The "b64" field MUST be set to "false" and the
"crit" field MUST contain at least "b64" as specified in [RFC7797]

To protect the request, the JWS header MUST contain the following
additional fields.

htm (string) The HTTP Method used to make this request, as an
uppercase ASCII string.

htu (string) The HTTP URI used for this request, including all path
and query components.

ts (integer) A timestamp of the request in integer seconds

at_hash (string) When to bind a request to an access token, the
access token hash value. Its value is the base64url encoding of
the left-most half of the hash of the octets of the ASCII
representation of the "access_token" value, where the hash
algorithm used is the hash algorithm used in the "alg" header
parameter of the JWS's JOSE Header. For instance, if the "alg" is
"RS256", hash the "access_token" value with SHA-256, then take the
left-most 128 bits and base64url encode them.

[[ See issue #106 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/106) ]]

The payload of the JWS object is the serialized body of the request,
and the object is signed according to detached JWS [RFC7797].

The RC client instance presents the signature in the Detached-JWS HTTP
Header field.
[[ See issue #107 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/107) ]]

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Detached-JWS: eyJiNjQiOmZhbHNlLCJhbGciOiJSUzI1NiIsImtpZCI6Inh5ei0xIn0.
.Y287HMtaY0EegEjoTd_04a4GC6qV48GgVbGKOhHdJnDtD0VuUlVjLfwne8AuUY3U7e8
9zUWwXLnAYK_BiS84M8EsrFvmv8yDLWzqveeIpcN5_ysveQnYt9Dqi32w6IOtAywkNUD
ZeJEdc3z5s9Ei8qrYFN2fxcu28YS4e8e_cHTK57003WJu-wFn2TJUmAbHuqvUsyTb-nz
YOKxuCKlqQItJF7E-cwSb_xULu-3f77BEU_vGbNYo5ZBa2B7UHO-kWNMSgbW2yeNNLbL
C18Kv80GF22Y7SbZt0e2TwnR2Aa2zksuUbntQ5c7a1-gxtnXzuIKa34OekrnyqE1hmVW
peQ

{
"resources": [
"dolphin-metadata"
],
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.foo",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "jwsd",
"key": {
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8
xYJCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPF
vpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyD
SWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS
63WYPHi_Ap2B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFe
kpdfWdiPQddQ6Y1cK2U3obvUg7w"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
},
}
}
If the request being made does not have a message body, such as an
HTTP GET, OPTIONS, or DELETE method, the JWS signature is calculated
over an empty payload.

When the server (AS or RS) receives the Detached-JWS header, it MUST
parse its contents as a detached JWS object. The HTTP Body is used
as the payload for purposes of validating the JWS, with no
transformations.

[[ See issue #108 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/108) ]]

8.2. Attached JWS

This method is indicated by "jws" in the "proof" field. A JWS
[RFC7515] signature object is created as follows:

To protect the request, the JWS header MUST contain the following
additional fields.

htm (string) The HTTP Method used to make this request, as an
uppercase ASCII string.

htu (string) The HTTP URI used for this request, including all path
and query components.

ts (integer) A timestamp of the request in integer seconds

[[ See issue #107 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/107) ]]

The payload of the JWS object is the JSON serialized body of the
request, and the object is signed according to JWS and serialized
into compact form [RFC7515].

The RC client instance presents the JWS as the body of the request along
with a content type of "application/jose". The AS MUST extract the
payload of the JWS and treat it as the request body for further
processing.

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/jose

eyJhbGciOiJSUzI1NiIsImtpZCI6IktBZ05wV2JSeXk5T
WYycmlrbDQ5OExUaE1ydmtiWldIVlNRT0JDNFZIVTQiLC
JodG0iOiJwb3N0IiwiaHR1IjoiL3R4IiwidHMiOjE2MDM
4MDA3ODN9.eyJjYXBhYmlsaXRpZXMiOltdLCJjbGllbnQ
iOnsia2V5Ijp7Imp3ayI6eyJrdHkiOiJSU0EiLCJlIjoi
QVFBQiIsImtpZCI6IktBZ05wV2JSeXk5TWYycmlrbDQ5O
ExUaE1ydmtiWldIVlNRT0JDNFZIVTQiLCJuIjoibGxXbU
hGOFhBMktOTGRteE9QM2t4RDlPWTc2cDBTcjM3amZoejk
0YTkzeG0yRk5xb1NQY1JaQVBkMGxxRFM4TjNVaWE1M2RC
MjNaNTlPd1k0YnBNX1ZmOEdKdnZwdExXbnhvMVB5aG1Qc
i1lY2RTQ1JRZFRjX1pjTUY0aFJWNDhxcWx2dUQwbXF0Y0
RiSWtTQkR2Y2NKbVpId2ZUcERIaW5UOHR0dmNWUDhWa0F
NQXE0a1ZhenhPcE1vSVJzb3lFcF9lQ2U1cFN3cUhvMGRh
Q1dOS1ItRXBLbTZOaU90ZWRGNE91bXQ4TkxLVFZqZllnR
khlQkRkQ2JyckVUZDR2Qk13RHRBbmpQcjNDVkN3d3gyYk
FRVDZTbHhGSjNmajJoaHlJcHE3cGM4clppYjVqTnlYS3d
mQnVrVFZZWm96a3NodC1Mb2h5QVNhS3BZVHA4THROWi13
In0sInByb29mIjoiandzIn0sIm5hbWUiOiJNeSBGaXN0I
ENsaWVudCIsInVyaSI6Imh0dHA6Ly9sb2NhbGhvc3QvY2
xpZW50L2NsaWVudElEIn0sImludGVyYWN0Ijp7ImNhbGx
iYWNrIjp7Im1ldGhvZCI6InJlZGlyZWN0Iiwibm9uY2Ui
OiJkOTAyMTM4ODRiODQwOTIwNTM4YjVjNTEiLCJ1cmkiO
iJodHRwOi8vbG9jYWxob3N0L2NsaWVudC9yZXF1ZXN0LW
RvbmUifSwicmVkaXJlY3QiOnRydWV9LCJyZXNvdXJjZXM
iOnsiYWN0aW9ucyI6WyJyZWFkIiwicHJpbnQiXSwibG9j
YXRpb25zIjpbImh0dHA6Ly9sb2NhbGhvc3QvcGhvdG9zI
l0sInR5cGUiOiJwaG90by1hcGkifSwic3ViamVjdCI6ey
JzdWJfaWRzIjpbImlzcy1zdWIiLCJlbWFpbCJdfX0.LUy
Z8_fERmxbYARq8kBYMwzcd8GnCAKAlo2ZSYLRRNAYWPrp
2XGLJOvg97WK1idf_LB08OJmLVsCXxCvn9mgaAkYNL_Zj
HcusBvY1mNo0E1sdTEr31CVKfC-6WrZCscb8YqE4Ayhh0
Te8kzSng3OkLdy7xN4xeKuHzpF7yGsM52JZ0cBcTo6WrY
EfGdr08AWQJ59ht72n3jTsmYNy9A6I4Wrvfgj3TNxmwYo
jpBAicfjnzA1UVcNm9F_xiSz1_y2tdH7j5rVqBMQife-k
9Ewk95vr3lurthenliYSNiUinVfoW1ybnaIBcTtP1_YCx
g_h1y-B5uZEvYNGCuoCqa6IQ

This example's JWS header decodes to:

{
"alg": "RS256",
"kid": "KAgNpWbRyy9Mf2rikl498LThMrvkbZWHVSQOBC4VHU4",
"htm": "post",
"htu": "/tx",
"ts": 1603800783
}

And the JWS body decodes to:

{
"capabilities": [],
"client": {
"key": {
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "KAgNpWbRyy9Mf2rikl498LThMrvkbZWHVSQOBC4VHU4",
"n": "llWmHF8XA2KNLdmxOP3kxD9OY76p0Sr37jfhz94a93xm2FNqoSPc
RZAPd0lqDS8N3Uia53dB23Z59OwY4bpM_Vf8GJvvptLWnxo1PyhmPr-ecd
SCRQdTc_ZcMF4hRV48qqlvuD0mqtcDbIkSBDvccJmZHwfTpDHinT8ttvcV
P8VkAMAq4kVazxOpMoIRsoyEp_eCe5pSwqHo0daCWNKR-EpKm6NiOtedF4
Oumt8NLKTVjfYgFHeBDdCbrrETd4vBMwDtAnjPr3CVCwwx2bAQT6SlxFJ3
fj2hhyIpq7pc8rZib5jNyXKwfBukTVYZozksht-LohyASaKpYTp8LtNZ-w"
},
"proof": "jws"
},
"name": "My Fist Client",
"uri": "http://localhost/client/clientID"
},
"interact": {
"callback": {
"method": "redirect",
"nonce": "d90213884b840920538b5c51",
"uri": "http://localhost/client/request-done"
},
"redirect": true
},
"resources": {
"actions": [
"read",
"print"
],
"locations": [
"http://localhost/photos"
],
"type": "photo-api"
},
"subject": {
"sub_ids": [
"iss_sub",
"email"
]
}
}
If the request being made does not have a message body, such as an
HTTP GET, OPTIONS, or DELETE method, the JWS signature is calculated
over an empty payload and passed in the "Detached-JWS" header as
described in Section 8.1.

[[ See issue #109 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/109) ]]

8.3. Mutual TLS

This method is indicated by "mtls" in the "proof" field. The RC client
instance presents its TLS client certificate during TLS negotiation
with the server (either AS or RS). The AS or RS takes the thumbprint
of the TLS client certificate presented during mutual TLS negotiation
and compares that thumbprint to the thumbprint presented by the RC
client instance application as described in [RFC8705] section 3.

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
SSL_CLIENT_CERT: MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3MDUGA1UEAwwuQmVz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{
"resources": [
"dolphin-metadata"
],
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.foo",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
},
"key": {
"proof": "mtls",
"cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3
MDUGA1UEAwwuQmVzcG9rZSBFbmdpbmVlcmluZyBSb290IENlcnRpZmljYXRlIEF1d
Ghvcml0eTELMAkGA1UECAwCTUExCzAJBgNVBAYTAlVTMRkwFwYJKoZIhvcNAQkBFg
pjYUBic3BrLmlvMRwwGgYDVQQKDBNCZXNwb2tlIEVuZ2luZWVyaW5nMQwwCgYDVQQ
LDANNVEkwHhcNMTkwNDEwMjE0MDI5WhcNMjQwNDA4MjE0MDI5WjB8MRIwEAYDVQQD
DAlsb2NhbGhvc3QxCzAJBgNVBAgMAk1BMQswCQYDVQQGEwJVUzEgMB4GCSqGSIb3D
QEJARYRdGxzY2xpZW50QGJzcGsuaW8xHDAaBgNVBAoME0Jlc3Bva2UgRW5naW5lZX
JpbmcxDDAKBgNVBAsMA01USTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggE
BAMmaXQHbs/wc1RpsQ6Orzf6rN+q2ijaZbQxD8oi+XaaN0P/gnE13JqQduvdq77Om
J4bQLokqsd0BexnI07Njsl8nkDDYpe8rNve5TjyUDCfbwgS7U1CluYenXmNQbaYND
OmCdHwwUjV4kKREg6DGAx22Oq7+VHPTeeFgyw4kQgWRSfDENWY3KUXJlb/vKR6lQ+
aOJytkvj8kVZQtWupPbvwoJe0na/ISNAOhL74w20DWWoDKoNltXsEtflNljVoi5nq
smZQcjfjt6LO0T7O1OX3Cwu2xWx8KZ3n/2ocuRqKEJHqUGfeDtuQNt6Jz79v/OTr8
puLWaD+uyk6NbtGjoQsCAwEAAaOBiTCBhjAJBgNVHRMEAjAAMAsGA1UdDwQEAwIF4
DBsBgNVHREEZTBjgglsb2NhbGhvc3SCD3Rsc2NsaWVudC5sb2NhbIcEwKgBBIERdG
xzY2xpZW50QGJzcGsuaW+GF2h0dHA6Ly90bHNjbGllbnQubG9jYWwvhhNzc2g6dGx
zY2xpZW50LmxvY2FsMA0GCSqGSIb3DQEBCwUAA4IBAQCKKv8WlLrT4Z5NazaUrYtl
TF+2v0tvZBQ7qzJQjlOqAcvxry/d2zyhiRCRS/v318YCJBEv4Iq2W3I3JMMyAYEe2
573HzT7rH3xQP12yZyRQnetdiVM1Z1KaXwfrPDLs72hUeELtxIcfZ0M085jLboXhu
fHI6kqm3NCyCCTihe2ck5RmCc5l2KBO/vAHF0ihhFOOOby1v6qbPHQcxAU6rEb907
/p6BW/LV1NCgYB1QtFSfGxowqb9FRIMD2kvMSmO0EMxgwZ6k6spa+jk0IsI3klwLW
9b+Tfn/daUbIDctxeJneq2anQyU2znBgQl6KILDSF4eaOqlBut/KNZHHazJh"
}
}

[[ See issue #110 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/110) ]]

8.4. Demonstration of Proof-of-Possession (DPoP)

This method is indicated by "dpop" in the "proof" field. The RC client
instance creates a Demonstration of Proof-of-Possession signature
header as described in [I-D.ietf-oauth-dpop] section 2. In addition
to the required fields, the DPoP body MUST also contain a digest of
the request body:

digest (string) Digest of the request body as the value of the
Digest header defined in [RFC3230].

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
DPoP: eyJ0eXAiOiJkcG9wK2p3dCIsImFsZyI6IlJTMjU2IiwiandrIjp7Imt0eSI6Il
JTQSIsImUiOiJBUUFCIiwia2lkIjoieHl6LWNsaWVudCIsImFsZyI6IlJTMjU2Iiwibi
I6Inp3Q1RfM2J4LWdsYmJIcmhlWXBZcFJXaVk5SS1uRWFNUnBablJySWpDczZiX2VteV
RrQmtEREVqU3lzaTM4T0M3M2hqMS1XZ3hjUGRLTkdaeUlvSDNRWmVuMU1LeXloUXBMSk
cxLW9MTkxxbTdwWFh0ZFl6U2RDOU8zLW9peXk4eWtPNFlVeU5aclJSZlBjaWhkUUNiT1
9PQzhRdWdtZzlyZ05ET1NxcHBkYU5lYXMxb3Y5UHhZdnhxcnoxLThIYTdna0QwMFlFQ1
hIYUIwNXVNYVVhZEhxLU9fV0l2WVhpY2c2STVqNlM0NFZOVTY1VkJ3dS1BbHluVHhRZE
1BV1AzYll4VlZ5NnAzLTdlVEpva3ZqWVRGcWdEVkRaOGxVWGJyNXlDVG5SaG5oSmd2Zj
NWakRfbWFsTmU4LXRPcUs1T1NEbEhUeTZnRDlOcWRHQ20tUG0zUSJ9fQ.eyJodHRwX21
ldGhvZCI6IlBPU1QiLCJodHRwX3VyaSI6Imh0dHA6XC9cL2hvc3QuZG9ja2VyLmludGV
ybmFsOjk4MzRcL2FwaVwvYXNcL3RyYW5zYWN0aW9uIiwiaWF0IjoxNTcyNjQyNjEzLCJ
qdGkiOiJIam9IcmpnbTJ5QjR4N2pBNXl5RyJ9.aUhftvfw2NoW3M7durkopReTvONng1
fOzbWjAlKNSLL0qIwDgfG39XUyNvwQ23OBIwe6IuvTQ2UBBPklPAfJhDTKd8KHEAfidN
B-LzUOzhDetLg30yLFzIpcEBMLCjb0TEsmXadvxuNkEzFRL-Q-QCg0AXSF1h57eAqZV8
SYF4CQK9OUV6fIWwxLDd3cVTx83MgyCNnvFlG_HDyim1Xx-rxV4ePd1vgDeRubFb6QWj
iKEO7vj1APv32dsux67gZYiUpjm0wEZprjlG0a07R984KLeK1XPjXgViEwEdlirUmpVy
T9tyEYqGrTfm5uautELgMls9sgSyE929woZ59elg

},
"proof": "dpop",
"key": {
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xYJ
CCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPFvpkTM
8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCH
e5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2
B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6Y
1cK2U3obvUg7w"
}
}
}
}

[[ See issue #111 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/111) ]]

8.5. HTTP Signing

This method is indicated by "httpsig" in the "proof" field. The RC
client instance creates an HTTP Signature header as described in
[I-D.ietf-httpbis-message-signatures] section 4. The RC client instance
MUST calculate and present the Digest header as defined in [RFC3230]
and include this header in the signature.

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Content-Length: 716
Signature: keyId="xyz-client", algorithm="rsa-sha256",
headers="(request-target) digest content-length",
signature="TkehmgK7GD/z4jGkmcHS67cjVRgm3zVQNlNrrXW32Wv7d
u0VNEIVI/dMhe0WlHC93NP3ms91i2WOW5r5B6qow6TNx/82/6W84p5jqF
YuYfTkKYZ69GbfqXkYV9gaT++dl5kvZQjVk+KZT1dzpAzv8hdk9nO87Xi
rj7qe2mdAGE1LLc3YvXwNxuCQh82sa5rXHqtNT1077fiDvSVYeced0UEm
rWwErVgr7sijtbTohC4FJLuJ0nG/KJUcIG/FTchW9rd6dHoBnY43+3Dzj
CIthXpdH5u4VX3TBe6GJDO6Mkzc6vB+67OWzPwhYTplUiFFV6UZCsDEeu
Sa/Ue1yLEAMg=="]}
Digest: SHA=oZz2O3kg5SEFAhmr0xEBbc4jEfo=

{
"resources": [
"dolphin-metadata"
],
"interact": {
"redirect": true,
"callback": {
"method": "push",
"uri": "https://client.foo",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
},
"proof": "httpsig",
"key": {
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_J
tffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-
y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-
ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx
06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttz
bMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6
Y1cK2U3obvUg7w"
}
}
}
}

When used to present an access token as in Section 7, the
Authorization header MUST be included in the signature.

8.6. OAuth Proof of Possession (PoP)

This method is indicated by "oauthpop" in the "proof" field. The RC
client instance creates an HTTP Authorization PoP header as described
in [I-D.ietf-oauth-signed-http-request] section 4, with the following
additional requirements:

* The "at" (access token) field MUST be omitted unless this method
is being used in conjunction with an access token as in Section 7.
[[ See issue #112 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/112) ]]

* The "b" (body hash) field MUST be calculated and supplied, unless
there is no entity body (such as a GET, OPTIONS, or DELETE
request).

* All components of the URL MUST be calculated and supplied

* The m (method) field MUST be supplied

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
PoP: eyJhbGciOiJSUzI1NiIsImp3ayI6eyJrdHkiOiJSU0EiLCJlIjoi
QVFBQiIsImtpZCI6Inh5ei1jbGllbnQiLCJhbGciOiJSUzI1NiIsIm4iO
iJ6d0NUXzNieC1nbGJiSHJoZVlwWXBSV2lZOUktbkVhTVJwWm5ScklqQ3
M2Yl9lbXlUa0JrRERFalN5c2kzOE9DNzNoajEtV2d4Y1BkS05HWnlJb0g
zUVplbjFNS3l5aFFwTEpHMS1vTE5McW03cFhYdGRZelNkQzlPMy1vaXl5
OHlrTzRZVXlOWnJSUmZQY2loZFFDYk9fT0M4UXVnbWc5cmdORE9TcXBwZ
GFOZWFzMW92OVB4WXZ4cXJ6MS04SGE3Z2tEMDBZRUNYSGFCMDV1TWFVYW
RIcS1PX1dJdllYaWNnNkk1ajZTNDRWTlU2NVZCd3UtQWx5blR4UWRNQVd
QM2JZeFZWeTZwMy03ZVRKb2t2allURnFnRFZEWjhsVVhicjV5Q1RuUmhu
aEpndmYzVmpEX21hbE5lOC10T3FLNU9TRGxIVHk2Z0Q5TnFkR0NtLVBtM
1EifX0.eyJwIjoiXC9hcGlcL2FzXC90cmFuc2FjdGlvbiIsImIiOiJxa0
lPYkdOeERhZVBTZnc3NnFjamtqSXNFRmxDb3g5bTU5NFM0M0RkU0xBIiw
idSI6Imhvc3QuZG9ja2VyLmludGVybmFsIiwiaCI6W1siQWNjZXB0Iiwi
Q29udGVudC1UeXBlIiwiQ29udGVudC1MZW5ndGgiXSwiVjQ2OUhFWGx6S
k9kQTZmQU5oMmpKdFhTd3pjSGRqMUloOGk5M0h3bEVHYyJdLCJtIjoiUE
9TVCIsInRzIjoxNTcyNjQyNjEwfQ.xyQ47qy8bu4fyK1T3Ru1Sway8wp6
5rfAKnTQQU92AUUU07I2iKoBL2tipBcNCC5zLH5j_WUyjlN15oi_lLHym
fPdzihtt8_Jibjfjib5J15UlifakjQ0rHX04tPal9PvcjwnyZHFcKn-So
Y3wsARn-gGwxpzbsPhiKQP70d2eG0CYQMA6rTLslT7GgdQheelhVFW29i
27NcvqtkJmiAG6Swrq4uUgCY3zRotROkJ13qo86t2DXklV-eES4-2dCxf
cWFkzBAr6oC4Qp7HnY_5UT6IWkRJt3efwYprWcYouOVjtRan3kEtWkaWr
G0J4bPVnTI5St9hJYvvh7FE8JirIg

[[ See issue #113 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/113) ]]

9. Discovery

By design, the protocol minimizes the need for any pre-flight
discovery. To begin a request, the RC client instance only needs to
know the endpoint of the AS and which keys it will use to sign the
request. Everything else can be negotiated dynamically in the course
of the protocol.

However, the AS can have limits on its allowed functionality. If the
RC
client instance wants to optimize its calls to the AS before making a
request, it MAY send an HTTP OPTIONS request to the grant request
endpoint to retrieve the server's discovery information. The AS MUST
respond with a JSON document containing the following information:

grant_request_endpoint (string) REQUIRED. The full URL of the AS's
grant request endpoint. This MUST match the URL the RC client
instance used to make the discovery request.

capabilities (array of strings) OPTIONAL. A list of the AS's
capabilities. The values of this result MAY be used by the RC client
instance in the capabilities section (Section 2.6) of the request.

interaction_methods (array of strings) OPTIONAL. A list of the AS's
interaction methods. The values of this list correspond to the
possible fields in the interaction section (Section 2.5) of the
request.

key_proofs (array strings) OPTIONAL. A list of the AS's supported
key proofing mechanisms. The values of this list correspond to
possible values of the "proof" field of the key section
(Section 2.3.2) of the request.

sub_ids (array of strings) OPTIONAL. A list of the AS's supported
identifiers. The values of this list correspond to possible
values of the subject identifier section (Section 2.2) of the
request.

assertions (array of strings) OPTIONAL. A list of the AS's
supported assertion formats. The values of this list correspond
to possible values of the subject assertion section (Section 2.2)
of the request.

The information returned from this method is for optimization
purposes only. The AS MAY deny any request, or any portion of a
request, even if it lists a capability as supported. For example, a
given RC client instance can be registered with the "mtls" key proofing
mechanism, but the AS also returns other proofing methods, then the
AS will deny a request from that RC client instance using a different
proofing mechanism.

10. Resource Servers

In some deployments, a resource server will need to be able to call
the AS for a number of functions.

[[ See issue #114 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/114) ]]

10.1. Introspecting a Token

When the RS receives an access token, it can call the introspection
endpoint at the AS to get token information. [[ See issue #115
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/115) ]]

+------+

+--------+ +------+ +------+
| RC Client |--(1)->| RS | | AS |
| |
|Instance| | |--(2)->| |
| | | |<-(3)--| |
| | | | +------+
| |<-(4)--| |
+------+
+--------+ +------+

1. The RC client instance calls the RS with its access token.

2. The RS introspects the access token value at the AS. The RS
signs the request with its own key (not the RC's client instance's key
or the token's key).

3. The AS validates the token value and the RC's client instance's
request and returns the introspection response for the token.

4. The RS fulfills the request from the RC. client instance.

The RS signs the request with its own key and sends the access token
as the body of the request.

POST /introspect HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
}

The AS responds with a data structure describing the token's current
state and any information the RS would need to validate the token's
presentation, such as its intended proofing mechanism and key
material.

Content-type: application/json

{
"active": true,
"resources": [
"dolphin-metadata", "some other thing"
],
"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeL...."
}
}
}
}

10.2. Deriving a downstream token

Some architectures require an RS to act as an RC a client instance and
request a derived access token for a secondary RS. This internal
token is issued in the context of the incoming access token.

+------+

+--------+ +-------+ +------+ +-------+
| RC Client |--(1)->| RS1 | | AS | | RS2 |
| |
|Instance| | |--(2)->| | | |
| | | |<-(3)--| | | |
| | | | +------+ | |
| | | | | |
| | | |-----------(4)------->| |
| | | |<----------(5)--------| |
| |<-(6)--| | | |
+------+
+--------+ +-------+ +-------+

1. The RC client instance calls RS1 with an access token.

2. RS1 presents that token to the AS to get a derived token for use
at RS2. RS1 indicates that it has no ability to interact with
the RO. RS1 signs its request with its own key, not the token's
key or the RC's client instance's key.

3. The AS returns a derived token to RS1 for use at RS2.

4. RS1 calls RS2 with the token from (3).

5. RS2 fulfills the call from RS1.

6. RS1 fulfills the call from RC. client instance.

If the RS needs to derive a token from one presented to it, it can
request one from the AS by making a token request as described in
Section 2 and presenting the existing access token's value in the
"existing_access_token" field.

The RS MUST identify itself with its own key and sign the request.

[[ See issue #116 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/116) ]]

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
],
"client": "7C7C4AZ9KHRS6X63AJAO",
"existing_access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0"
}

The AS responds with a token as described in Section 3.

10.3. Registering a Resource Handle

If the RS needs to, it can post a set of resources as described in
Section 2.1.1 to the AS's resource registration endpoint.

The RS MUST identify itself with its own key and sign the request.

POST /resource HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

}

The AS responds with a handle appropriate to represent the resources
list that the RS presented.

Content-type: application/json

{
"resource_handle": "FWWIKYBQ6U56NL1"
}

The RS MAY make this handle available as part of a response
(Section 10.4) or as documentation to developers.

[[ See issue #117 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/117) ]]

10.4. Requesting Resources With Insufficient Access

If the RC client instance calls an RS without an access token, or with
an invalid access token, the RS MAY respond to the RC client instance
with an authentication header indicating that GNAP needs to be used
to access the resource. The address of the GNAP endpoint MUST be
sent in the "as_uri" parameter. The RS MAY additionally return a
resource reference that the RC client instance MAY use in its resource
request (Section 2.1). This resource reference handle SHOULD be
sufficient for at least the action the RC client instance was attempting
to take at the RS. The RS MAY use the dynamic resource handle
request (Section 10.3) to register a new resource handle, or use a
handle that has been pre-configured to represent what the AS is
protecting. The content of this handle is opaque to the RS and the RC.
client instance.

WWW-Authenticate: GNAP as_uri=http://server.example/tx,resource=FWWIKYBQ6U56NL1

The RC client instance then makes a call to the "as_uri" as described in
Section 2, with the value of "resource" as one of the members of a
"resources" array Section 2.1.1. The RC client instance MAY request
additional resources and other information, and MAY request multiple
access tokens.

[[ See issue #118 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/118) ]]

11. Acknowledgements

The author editors would like to thank the feedback of the following
individuals for their reviews, implementations, and contributions:
Aaron Parecki, Annabelle Backman, Dick Hardt, Dmitri Zagidulin,
Dmitry Barinov, Fabien Imbault, Francis Pouatcha, George Fletcher,
Haardik Haardik, Hamid Massaoud, Jacky Yuan, Joseph Heenan, Justin
Richer, Kathleen Moriarty, Mike Jones, Mike Varley, Nat Sakimura,
Takahiko Kawasaki, Takahiro Tsuchiya.

The editors would also like to thank the GNAP working group design
team of Kathleen Moriarty, Fabien Imbault, Dick Hardt, Mike Jones,
and Justin Richer, who incorporated elements from the XAuth and XYZ
proposals to create the first version of this document.

In particular, addition, the author editors would like to thank Aaron Parecki and Mike
Jones for insights into how to integrate identity and authentication
systems into the core protocol, and to Justin Richer and Dick Hardt for
the use cases, diagrams, and insights provided in the XYZ and XAuth proposal
proposals that have been incorporated here. The author editors would like
to especially thank Mike Varley and the team at SecureKey for
feedback and development of early versions of the XYZ protocol that
fed into this standards work.

12. IANA Considerations

[[ TBD: There are a lot of items in the document that are expandable
through the use of value registries. ]]

13. Security Considerations

[[ TBD: There are a lot of security considerations to add. ]]

All requests have to be over TLS or equivalent as per [BCP195]. Many
handles act as shared secrets, though they can be combined with a
requirement to provide proof of a key as well.

14. Privacy Considerations

[[ TBD: There are a lot of privacy considerations to add. ]]

Handles are passed between parties and therefore should not contain
any private data.

When user information is passed to the RC, client instance, the AS needs
to make sure that it has the permission to do so.

15. Normative References

[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", May 2015,
<http://www.rfc-editor.org/info/bcp195>.

[I-D.ietf-httpbis-message-signatures]
Backman, A., Richer, J., and M. Sporny, "Signing HTTP
Messages", Work in Progress, Internet-Draft, draft-ietf-
httpbis-message-signatures-00, 10 April
httpbis-message-signatures-01, 17 November 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-httpbis-
message-signatures-00.txt>.
message-signatures-01.txt>.

[I-D.ietf-oauth-dpop]
Fett, D., Campbell, B., Bradley, J., Lodderstedt, T.,
Jones, M., and D. Waite, "OAuth 2.0 Demonstration of
Proof-of-Possession Demonstrating Proof-
of-Possession at the Application Layer (DPoP)", Work in
Progress, Internet-Draft, draft-ietf-oauth-dpop-01, 1
May draft-ietf-oauth-dpop-02, 18
November 2020, <http://www.ietf.org/internet-drafts/draft-ietf-
oauth-dpop-01.txt>. <http://www.ietf.org/internet-drafts/draft-
ietf-oauth-dpop-02.txt>.

[I-D.ietf-oauth-signed-http-request]
Richer, J., Bradley, J., and H. Tschofenig, "A Method for
Signing HTTP Requests for OAuth", Work in Progress,
Internet-Draft, draft-ietf-oauth-signed-http-request-03, 8
August 2016, <http://www.ietf.org/internet-drafts/draft-
ietf-oauth-signed-http-request-03.txt>.

[I-D.ietf-secevent-subject-identifiers]
Backman, A. and M. Scurtescu, "Subject Identifiers for
Security Event Tokens", Work in Progress, Internet-Draft,
draft-ietf-secevent-subject-identifiers-06, 4 September
2020, <http://www.ietf.org/internet-drafts/draft-ietf-
secevent-subject-identifiers-06.txt>.

[OIDC] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", November 2014,
<https://openiD.net/specs/openiD-connect-core-1_0.html>.

[OIDC4IA] Lodderstedt, T. and D. Fett, "OpenID Connect for Identity
Assurance 1.0", October 2019, <https://openid.net/specs/
openid-connect-4-identity-assurance-1_0.html>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3230] Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
RFC 3230, DOI 10.17487/RFC3230, January 2002,
<https://www.rfc-editor.org/info/rfc3230>.

[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.

[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.

[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/info/rfc6750>.

[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.

[RFC7797] Jones, M., "JSON Web Signature (JWS) Unencoded Payload
Option", RFC 7797, DOI 10.17487/RFC7797, February 2016,
<https://www.rfc-editor.org/info/rfc7797>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.

[RFC8693] Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J.,
and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693,
DOI 10.17487/RFC8693, January 2020,
<https://www.rfc-editor.org/info/rfc8693>.

[RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
and Certificate-Bound Access Tokens", RFC 8705,
DOI 10.17487/RFC8705, February 2020,
<https://www.rfc-editor.org/info/rfc8705>.

Appendix A. Document History

* -03

- Changed "resource client" terminology to separate "client
instance" and "client software".

* -02

- Moved all "editor's note" items to GitHub Issues.

- Added JSON types to fields.

- Changed "GNAP Protocol" to "GNAP".

- Editorial fixes.

* -01
- "updated_at" subject info timestamp now in ISO 8601 string
format.

- Editorial fixes.

- Added Aaron and Fabien as document authors.

* -00

- Initial working group draft.

Appendix B. Component Data Models

While different implementations of this protocol will have different
realizations of all the components and artifacts enumerated here, the
nature of the protocol implies some common structures and elements
for certain components. This appendix seeks to enumerate those
common elements.

TBD: Client has keys, allowed requested resources, identifier(s),
allowed requested subjects, allowed

TBD: AS has "grant endpoint", interaction endpoints, store of trusted
client keys, policies

TBD: Token has RO, user, client, resource list, RS list,

Appendix C. Example Protocol Flows

The protocol defined in this specification provides a number of
features that can be combined to solve many different kinds of
authentication scenarios. This section seeks to show examples of how
the protocol would be applied for different situations.

Some longer fields, particularly cryptographic information, have been
truncated for display purposes in these examples.

C.1. Redirect-Based User Interaction

In this scenario, the user is the RO and has access to a web browser,
and the client instance can take front-channel callbacks on the same
device as the user. This combination is analogous to the OAuth 2
Authorization Code grant type.

The client instance initiates the request to the AS. Here the client
instance identifies itself using its public key.

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}
],
"client": {
"key": {
"proof": "jwsd",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
}
}
},
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
}
The AS processes the request and determines that the RO needs to
interact. The AS returns the following response giving the client
instance the information it needs to connect. The AS has also
indicated to the client instance that it can use the given instance
identifier to identify itself in future requests (Section 2.3.1).

Content-type: application/json

{
"interact": {
"redirect": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
"callback": "MBDOFXG4Y5CVJCX821LH"
}
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/continue"
},
"instance_id": "7C7C4AZ9KHRS6X63AJAO"
}

The client instance saves the response and redirects the user to the
interaction_url by sending the following HTTP message to the user's
browser.

HTTP 302 Found
Location: https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ

The user's browser fetches the AS's interaction URL. The user logs
in, is identified as the RO for the resource being requested, and
approves the request. Since the AS has a callback parameter, the AS
generates the interaction reference, calculates the hash, and
redirects the user back to the client instance with these additional
values added as query parameters.

HTTP 302 Found
Location: https://client.example.net/return/123455
?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
&interact_ref=4IFWWIKYBC2PQ6U56NL1
The client instance receives this request from the user's browser.
The client instance ensures that this is the same user that was sent
out by validating session information and retrieves the stored
pending request. The client instance uses the values in this to
validate the hash parameter. The client instance then calls the
continuation URL and presents the handle and interaction reference in
the request body. The client instance signs the request as above.

POST /continue HTTP/1.1
Host: server.example.com
Content-type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}

The AS retrieves the pending request based on the handle and issues a
bearer access token and returns this to the client. client instance.

Content-type: application/json

{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"key": false,
"manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
"resources": [{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}]
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/continue"
}
}

C.2. Secondary Device Interaction

In this scenario, the user does not have access to a web browser on
the device and must use a secondary device to interact with the AS.
The client instance can display a user code or a printable QR code.
The client prefers a short URL if one is available, with a maximum of 255
characters in length. The instance is not able to accept callbacks from the AS and
needs to poll for updates while waiting for the user to authorize the
request.

The client instance initiates the request to the AS.

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
"dolphin-metadata", "some other thing"
],
"client": "7C7C4AZ9KHRS6X63AJAO",
"interact": {
"redirect": 255, true,
"user_code": true
}
}

The AS processes this and determines that the RO needs to interact.
The AS supports both long and short redirect URIs and user codes for interaction, so
it includes both. Since there is no "callback" the AS does not
include a nonce, but does include a "wait" parameter on the
continuation section because it expects the client instance to poll
for results.

Content-type: application/json

{
"interact": {
"redirect": "https://srv.ex/MXKHQ",
"user_code": {
"code": "A1BC-3DFF",
"url": "https://srv.ex/device"
}
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/continue/80UPRY5NM33OMUKMKSKU", "https://server.example.com/continue/VGJKPTKC50",
"wait": 60
}
}

The client instance saves the response and displays the user code
visually on its screen along with the static device URL. The client
instance also displays the short interaction URL as a QR code to be
scanned.

If the user scans the code, they are taken to the interaction
endpoint and the AS looks up the current pending request based on the
incoming URL. If the user instead goes to the static page and enters
the code manually, the AS looks up the current pending request based
on the value of the user code. In both cases, the user logs in, is
identified as the RO for the resource being requested, and approves
the request. Once the request has been approved, the AS displays to
the user a message to return to their device.

Meanwhile, the client instance periodically polls the AS every 60
seconds at the continuation URL. The client instance signs the
request using the same key and method that it did in the first
request.

POST /continue/80UPRY5NM33OMUKMKSKU /continue/VGJKPTKC50 HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

The AS retrieves the pending request based on the handle and
determines that it has not yet been authorized. The AS indicates to
the client instance that no access token has yet been issued but it
can continue to call after another 60 second timeout.

Content-type: application/json

{
"continue": {
"access_token": {
"value": "G7YQT4KQQ5TZY9SLSS5E",
"key": true
},
"uri": "https://server.example.com/continue/BI9QNW6V9W3XFJK4R02D", "https://server.example.com/continue/ATWHO4Q1WV",
"wait": 60
}
}

Note that the continuation URL has and access token have been rotated
since it was they were used by the client instance to make this call. The
client instance polls the continuation URL after a 60 second timeout
using the this new handle. information.

POST /continue/BI9QNW6V9W3XFJK4R02D /continue/ATWHO4Q1WV HTTP/1.1
Host: server.example.com
Authorization: GNAP G7YQT4KQQ5TZY9SLSS5E
Detached-JWS: ejy0...

The AS retrieves the pending request based on the URL, URL and access
token, determines that it has been approved, and issues an access token.
token for the client to use at the RS.

Content-type: application/json

Appendix D. No User Involvement

In this scenario, the client instance is requesting access on its own
behalf, with no user to interact with.

The client instance creates a request to the AS, identifying itself
with its public key and using MTLS to make the request.

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json

{
"resources": [
"backend service", "nightly-routine-3"
],
"client": {
"key": {
"proof": "mtls",
"cert#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
}
}
}

The AS processes this and determines that the client instance can ask
for the requested resources and issues an access token.

Content-type: application/json

{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"key": true,
"manage": "https://server.example.com/token",
"resources": [
"backend service", "nightly-routine-3"
]
}
}

D.1. Asynchronous Authorization

In this scenario, the client instance is requesting on behalf of a
specific RO, but has no way to interact with the user. The AS can
asynchronously reach out to the RO for approval in this scenario.

The client instance starts the request at the AS by requesting a set
of resources. The client instance also identifies a particular user.

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata",
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
},
"some other thing"
],
"client": "7C7C4AZ9KHRS6X63AJAO",
"user": {
"sub_ids": [ {
"subject_type": "email",
"email": "user@example.com"
} ]
}
}

The AS processes this and determines that the RO needs to interact.
The AS determines that it can reach the identified user
asynchronously and that the identified user does have the ability to
approve this request. The AS indicates to the client instance that
it can poll for continuation.

Content-type: application/json

{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
"key": true
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}

The AS reaches out to the RO and prompts them for consent. In this
example, the AS has an application that it can push notifications in
to for the specified account.

Meanwhile, the client instance periodically polls the AS every 60
seconds at the continuation URL.

POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Detached-JWS: ejy0...

Content-type: application/json

{
"continue": {
"access_token": {
"value": "BI9QNW6V9W3XFJK4R02D",
"key": true
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}

Note that the continuation handle has been rotated since it was used
by the client instance to make this call. The client instance polls
the continuation URL after a 60 second timeout using the new handle.

POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP BI9QNW6V9W3XFJK4R02D
Detached-JWS: ejy0...

The AS retrieves the pending request based on the handle and
determines that it has been approved and it issues an access token.

Content-type: application/json

D.2. Applying OAuth 2 Scopes and Client IDs

While GNAP is not designed to be directly compatible with OAuth 2
[RFC6749], considerations have been made to enable the use of OAuth 2
concepts and constructs more smoothly within GNAP.

In this scenario, the client developer has a "client_id" and set of
"scope" values from their OAuth 2 system and wants to apply them to
the new protocol. Traditionally, the OAuth 2 client developer would
put their "client_id" and "scope" values as parameters into a
redirect request to the authorization endpoint.

HTTP 302 Found
Location: https://server.example.com/authorize
?client_id=7C7C4AZ9KHRS6X63AJAO
&scope=read%20write%20dolphin
&redirect_uri=https://client.example.net/return
&response_type=code
&state=123455

Now the developer wants to make an analogous request to the AS using
the new protocol.
GNAP. To do so, the client instance makes an HTTP POST and places
the OAuth 2 values in the appropriate places.

POST /tx HTTP/1.1
Host: server.example.com
Content-type: application/json
Detached-JWS: ejy0...

{
"resources": [
"read", "write", "dolphin"
],
"client": "7C7C4AZ9KHRS6X63AJAO",
"interact": {
"redirect": true,
"callback": {
"method": "redirect",
"uri": "https://client.example.net/return?state=123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
}

The client_id can be used to identify the client's client instance's keys that
it uses for authentication, the scopes represent resources that the
client instance is requesting, and the "redirect_uri" and "state"
value are pre-combined into a "callback" URI that can be unique per
request. The client instance additionally creates a nonce to protect
the callback, separate from the state parameter that it has added to
its return URL.

From here, the protocol continues as above.

Appendix E. JSON Structures and Polymorphism

GNAP makes use of polymorphism within the JSON [RFC8259] structures
used for the protocol. Each portion of this protocol is defined in
terms of the JSON data type that its values can take, whether it's a
string, object, array, boolean, or number. For some fields,
different data types offer different descriptive capabilities and are
used in different situations for the same field. Each data type
provides a different syntax to express the same underlying semantic
protocol element, which allows for optimization and simplification in
many common cases.

Even though JSON is often used to describe strongly typed structures,
JSON on its own is naturally polymorphic. In JSON, the named members
of an object have no type associated with them, and any data type can
be used as the value for any member. In practice, each member has a
semantic type that needs to make sense to the parties creating and
consuming the object. Within this protocol, each object member is
defined in terms of its semantic content, and this semantic content
might have expressions in different concrete data types for different
specific purposes. Since each object member has exactly one value in
JSON, each data type for an object member field is naturally mutually
exclusive with other data types within a single JSON object.

For example, a resource request for a single access token is composed
of an array of resource request descriptions while a request for
multiple access tokens is composed of an object whose member values
are all arrays. Both of these represent requests for access, but the
difference in syntax allows the RC client instance and AS to
differentiate between the two request types in the same request.

Another form of polymorphism in JSON comes from the fact that the
values within JSON arrays need not all be of the same JSON data type.
However, within this protocol, each element within the array needs to
be of the same kind of semantic element for the collection to make
sense, even when the data types are different from each other.

For example, each aspect of a resource request can be described using
an object with multiple dimensional components, or the aspect can be
requested using a string. In both cases, the resource request is
being described in a way that the AS needs to interpret, but with
different levels of specificity and complexity for the RC client
instance to deal with. An API designer can provide a set of common
access scopes as simple strings but still allow RC developers to
specify custom access when needed for more complex APIs.

Extensions to this specification can use different data types for
defined fields, but each extension needs to not only declare what the
data type means, but also provide justification for the data type
representing the same basic kind of thing it extends. For example,
an extension declaring an "array" representation for a field would
need to explain how the array represents something akin to the non-
array element that it is replacing.

Authors' Addresses

Justin Richer (editor)
Bespoke Engineering

Email: ietf@justin.richer.org
URI: https://bspk.io/

Aaron Parecki
Okta
Email: aaron@parecki.com
URI: https://aaronparecki.com

Fabien Imbault
acert.io

Email: fabien.imbault@acert.io
URI: https://acert.io/