draft-ietf-oauth-mtls-07.txt   draft-ietf-oauth-mtls-08.txt 
OAuth Working Group B. Campbell OAuth Working Group B. Campbell
Internet-Draft Ping Identity Internet-Draft Ping Identity
Intended status: Standards Track J. Bradley Intended status: Standards Track J. Bradley
Expires: August 2, 2018 Yubico Expires: November 7, 2018 Yubico
N. Sakimura N. Sakimura
Nomura Research Institute Nomura Research Institute
T. Lodderstedt T. Lodderstedt
YES Europe AG YES Europe AG
January 29, 2018 May 6, 2018
OAuth 2.0 Mutual TLS Client Authentication and Certificate Bound Access OAuth 2.0 Mutual TLS Client Authentication and Certificate Bound Access
Tokens Tokens
draft-ietf-oauth-mtls-07 draft-ietf-oauth-mtls-08
Abstract Abstract
This document describes Transport Layer Security (TLS) mutual This document describes OAuth client authentication and certificate
authentication using X.509 certificates as a mechanism for OAuth bound access tokens using mutual Transport Layer Security (TLS)
client authentication to the authorization sever as well as for authentication with X.509 certificates. OAuth clients are provided a
certificate bound sender constrained access tokens as a method for a mechanism for authentication to the authorization sever using mutual
protected resource to ensure that an access token presented to it by TLS, based on either single certificates or public key infrastructure
a given client was issued to that client by the authorization server. (PKI). OAuth authorization servers are provided a mechanism for
binding access tokens to a client's mutual TLS certificate, and OAuth
protected resources are provided a method for ensuring that such an
access token presented to it was issued to the client presenting the
token.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 2, 2018. This Internet-Draft will expire on November 7, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation and Conventions . . . . . . . . . . 3 1.1. Requirements Notation and Conventions . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Mutual TLS for OAuth Client Authentication . . . . . . . . . 4 2. Mutual TLS for OAuth Client Authentication . . . . . . . . . 4
2.1. PKI Mutual TLS OAuth Client Authentication Method . . . . 5 2.1. PKI Mutual TLS OAuth Client Authentication Method . . . . 5
2.1.1. PKI Authentication Method Metadata Value . . . . . . 5 2.1.1. PKI Authentication Method Metadata Value . . . . . . 5
2.1.2. Client Registration Metadata . . . . . . . . . . . . 5 2.1.2. Client Registration Metadata . . . . . . . . . . . . 5
2.2. Self-Signed Certificate Mutual TLS OAuth Client 2.2. Self-Signed Certificate Mutual TLS OAuth Client
Authentication Method . . . . . . . . . . . . . . . . . . 6 Authentication Method . . . . . . . . . . . . . . . . . . 6
2.2.1. Self-Signed Certificate Authentication Method 2.2.1. Self-Signed Certificate Authentication Method
Metadata Value . . . . . . . . . . . . . . . . . . . 6 Metadata Value . . . . . . . . . . . . . . . . . . . 6
2.2.2. Client Registration Metadata . . . . . . . . . . . . 6 2.2.2. Client Registration Metadata . . . . . . . . . . . . 6
3. Mutual TLS Sender Constrained Resources Access . . . . . . . 7 3. Mutual TLS Client Certificate Bound Access Tokens . . . . . . 7
3.1. X.509 Certificate Thumbprint Confirmation Method for JWT 7 3.1. X.509 Certificate Thumbprint Confirmation Method for JWT 7
3.2. Confirmation Method for Token Introspection . . . . . . . 8 3.2. Confirmation Method for Token Introspection . . . . . . . 8
3.3. Authorization Server Metadata . . . . . . . . . . . . . . 9 3.3. Authorization Server Metadata . . . . . . . . . . . . . . 9
3.4. Client Registration Metadata . . . . . . . . . . . . . . 9 3.4. Client Registration Metadata . . . . . . . . . . . . . . 10
4. Implementation Considerations . . . . . . . . . . . . . . . . 10 4. Implementation Considerations . . . . . . . . . . . . . . . . 10
4.1. Authorization Server . . . . . . . . . . . . . . . . . . 10 4.1. Authorization Server . . . . . . . . . . . . . . . . . . 10
4.2. Resource Server . . . . . . . . . . . . . . . . . . . . . 10 4.2. Resource Server . . . . . . . . . . . . . . . . . . . . . 10
4.3. Sender Constrained Access Tokens Without Client 4.3. Certificate Bound Access Tokens Without Client
Authentication . . . . . . . . . . . . . . . . . . . . . 10 Authentication . . . . . . . . . . . . . . . . . . . . . 10
4.4. Certificate Bound Access Tokens . . . . . . . . . . . . . 11 4.4. Certificate Bound Access Tokens . . . . . . . . . . . . . 11
4.5. Implicit Grant Unsupported . . . . . . . . . . . . . . . 11 4.5. Implicit Grant Unsupported . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 4.6. TLS Termination . . . . . . . . . . . . . . . . . . . . . 12
5.1. TLS Versions and Best Practices . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5.1. TLS Versions and Best Practices . . . . . . . . . . . . . 12
5.2. X.509 Certificate Spoofing . . . . . . . . . . . . . . . 12 5.2. X.509 Certificate Spoofing . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 5.3. X.509 Certificate Parsing and Validation Complexity . . . 12
6.1. JWT Confirmation Methods Registration . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6.2. OAuth Authorization Server Metadata Registration . . . . 12 6.1. JWT Confirmation Methods Registration . . . . . . . . . . 13
6.3. Token Endpoint Authentication Method Registration . . . . 12 6.2. OAuth Authorization Server Metadata Registration . . . . 13
6.4. OAuth Token Introspection Response Registration . . . . . 13 6.3. Token Endpoint Authentication Method Registration . . . . 13
6.5. OAuth Dynamic Client Registration Metadata Registration . 13 6.4. OAuth Token Introspection Response Registration . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.5. OAuth Dynamic Client Registration Metadata Registration . 14
7.1. Normative References . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Normative References . . . . . . . . . . . . . . . . . . 14
7.2. Informative References . . . . . . . . . . . . . . . . . 15 7.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Relationship to Token Binding . . . . . . . . . . . 16 Appendix A. Relationship to Token Binding . . . . . . . . . . . 17
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 16 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 17
Appendix C. Document(s) History . . . . . . . . . . . . . . . . 17 Appendix C. Document(s) History . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
This document describes Transport Layer Security (TLS) mutual This document describes OAuth client authentication and certificate
authentication using X.509 certificates as a mechanism for OAuth bound access tokens using mutual TLS [RFC5246] authentication with
client authentication to the authorization sever as well as for X.509 certificates. OAuth clients are provided mechanisms for
sender constrained access to OAuth protected resources. authentication to the authorization sever using mutual TLS. OAuth
authorization servers are provided a mechanism for binding access
tokens to a client's mutual TLS certificate, and OAuth protected
resources are provided a method for ensuring that such an access
token presented to it was issued to the client presenting the token.
The OAuth 2.0 Authorization Framework [RFC6749] defines a shared The OAuth 2.0 Authorization Framework [RFC6749] defines a shared
secret method of client authentication but also allows for the secret method of client authentication but also allows for the
definition and use of additional client authentication mechanisms definition and use of additional client authentication mechanisms
when interacting directly with the authorization server. This when interacting directly with the authorization server. This
document describes an additional mechanism of client authentication document describes an additional mechanism of client authentication
utilizing mutual TLS [RFC5246] certificate-based authentication, utilizing mutual TLS certificate-based authentication, which provides
which provides better security characteristics than shared secrets. better security characteristics than shared secrets. While [RFC6749]
While [RFC6749] documents client authentication for requests to the documents client authentication for requests to the token endpoint,
token endpoint, extensions to OAuth 2.0 (such as Introspection extensions to OAuth 2.0 (such as Introspection [RFC7662] and
[RFC7662] and Revocation [RFC7009]) define endpoints that also Revocation [RFC7009]) define endpoints that also utilize client
utilize client authentication and the mutual TLS methods defined authentication and the mutual TLS methods defined herein are
herein are applicable to those endpoints as well. applicable to those endpoints as well.
Mutual TLS sender constrained access to protected resources ensures Mutual TLS certificate bound access tokens ensure that only the party
that only the party in possession of the private key corresponding to in possession of the private key corresponding to the certificate can
the certificate can utilize the access token to get access to the utilize the token to access the associated resources. Such a
associated resources. Such a constraint is unlike the case of the constraint is sometimes referred to as key confirmation, proof-of-
basic bearer token described in [RFC6750], where any party in possession, or holder-of-key and is unlike the case of the bearer
possession of the access token can use it to access the associated token described in [RFC6750], where any party in possession of the
resources. Mutual TLS sender constrained access binds the access access token can use it to access the associated resources. Binding
token to the client's certificate thus preventing the use of stolen an access token to the client's certificate prevents the use of
access tokens or replay of access tokens by unauthorized parties. stolen access tokens or replay of access tokens by unauthorized
parties.
Mutual TLS sender constrained access tokens and mutual TLS client Mutual TLS certificate bound access tokens and mutual TLS client
authentication are distinct mechanisms, which are complementary but authentication are distinct mechanisms, which are complementary but
don't necessarily need to be deployed together. don't necessarily need to be deployed or used together.
1.1. Requirements Notation and Conventions 1.1. Requirements Notation and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Terminology 1.2. Terminology
This specification uses the following phrases interchangeably: Mutual TLS refers to the process whereby a client presents its X.509
certificate and proves possession of the corresponding private key to
Transport Layer Security (TLS) Mutual Authentication a server when negotiating a TLS session. In TLS 1.2 [RFC5246] this
requires the client to send Client Certificate and Certificate Verify
Mutual TLS messages during the TLS handshake and for the server to verify these
messages.
These phrases all refer to the process whereby a client presents its
X.509 certificate and proves possession of the corresponding private
key to a server when negotiating a TLS session. In TLS 1.2 [RFC5246]
this requires the client to send Client Certificate and Certificate
Verify messages during the TLS handshake and for the server to verify
these messages.
2. Mutual TLS for OAuth Client Authentication 2. Mutual TLS for OAuth Client Authentication
This section defines, as an extension of OAuth 2.0, Section 2.3 This section defines, as an extension of OAuth 2.0, Section 2.3
[RFC6749], two distinct methods of using mutual TLS X.509 client [RFC6749], two distinct methods of using mutual TLS X.509 client
certificates as client credentials. The requirement of mutual TLS certificates as client credentials. The requirement of mutual TLS
for client authentication is determined by the authorization server for client authentication is determined by the authorization server
based on policy or configuration for the given client (regardless of based on policy or configuration for the given client (regardless of
whether the client was dynamically registered or statically whether the client was dynamically registered, statically configured,
configured or otherwise established). or otherwise established).
In order to utilize TLS for OAuth client authentication, the TLS In order to utilize TLS for OAuth client authentication, the TLS
connection between the client and the authorization server MUST have connection between the client and the authorization server MUST have
been established or reestablished with mutual X.509 certificate been established or reestablished with mutual TLS X.509 certificate
authentication (i.e. the Client Certificate and Certificate Verify authentication (i.e. the Client Certificate and Certificate Verify
messages are sent during the TLS Handshake [RFC5246]). messages are sent during the TLS Handshake [RFC5246]).
For all requests to the authorization server utilizing mutual TLS For all requests to the authorization server utilizing mutual TLS
client authentication, the client MUST include the "client_id" client authentication, the client MUST include the "client_id"
parameter, described in OAuth 2.0, Section 2.2 [RFC6749]. The parameter, described in OAuth 2.0, Section 2.2 [RFC6749]. The
presence of the "client_id" parameter enables the authorization presence of the "client_id" parameter enables the authorization
server to easily identify the client independently from the content server to easily identify the client independently from the content
of the certificate. The authorization server can locate the client of the certificate. The authorization server can locate the client
configuration using the client identifier and check the certificate configuration using the client identifier and check the certificate
presented in the TLS Handshake against the expected credentials for presented in the TLS Handshake against the expected credentials for
that client. The authorization server MUST enforce some method of that client. The authorization server MUST enforce the binding of a
binding a certificate to a client. Sections Section 2.1 and certificate to a specific client as described in either Section 2.1
Section 2.2 below define two ways of binding a certificate to a or Section 2.2 below.
client as two distinct client authentication methods.
2.1. PKI Mutual TLS OAuth Client Authentication Method 2.1. PKI Mutual TLS OAuth Client Authentication Method
The PKI (public key infrastructure) method of mutual TLS OAuth client The PKI (public key infrastructure) method of mutual TLS OAuth client
authentication uses a subject distinguished name (DN) and validated authentication uses a subject distinguished name (DN) and validated
certificate chain to identify the client. The TLS handshake is certificate chain to identify the client. The TLS handshake is
utilized to validate the client's possession of the private key utilized to validate the client's possession of the private key
corresponding to the public key in the certificate and to validate corresponding to the public key in the certificate and to validate
the corresponding certificate chain. The client is successfully the corresponding certificate chain. The client is successfully
authenticated if the subject information in the certificate matches authenticated if the subject information in the certificate matches
the expected DN configured or registered for that particular client. the expected DN configured or registered for that particular client
The PKI method facilitates the way X.509 certificates are (note that a predictable treatment of DN values, such as the
traditionally being used for authentication. It also allows the distinguishedNameMatch rule from [RFC4517], is needed in comparing
client to rotate its X.509 certificates without the need to modify the certificate's subject DN to the client's registered DN). If and
its respective authentication data at the authorization server by how to check a certificate's revocation status is a deployment
obtaining a new certificate with the same subject DN from a trusted decision at the discretion of the authorization server. The PKI
certificate authority (CA). method facilitates the way X.509 certificates are traditionally being
used for authentication. It also allows the client to rotate its
X.509 certificates without the need to modify its respective
authentication data at the authorization server by obtaining a new
certificate with the same subject DN from a trusted certificate
authority (CA).
2.1.1. PKI Authentication Method Metadata Value 2.1.1. PKI Authentication Method Metadata Value
The "OAuth Token Endpoint Authentication Methods" registry For the PKI method of mutual TLS client authentication, this
[IANA.OAuth.Parameters] contains values, each of which specify a specification defines and registers the following authentication
method of authenticating a client to the authorization server. The method metadata value into the "OAuth Token Endpoint Authentication
values are used to indicate supported and utilized client Methods" registry [IANA.OAuth.Parameters].
authentication methods in authorization server metadata, such as
OpenID Connect Discovery [OpenID.Discovery] and OAuth 2.0
Authorization Server Metadata [I-D.ietf-oauth-discovery], and in the
OAuth 2.0 Dynamic Client Registration Protocol [RFC7591]. For the
PKI method of mutual TLS client authentication, this specification
defines and registers the following authentication method metadata
value.
tls_client_auth tls_client_auth
Indicates that client authentication to the authorization server Indicates that client authentication to the authorization server
will occur with mutual TLS utilizing the PKI method of associating will occur with mutual TLS utilizing the PKI method of associating
a certificate to a client. a certificate to a client.
2.1.2. Client Registration Metadata 2.1.2. Client Registration Metadata
The following metadata parameter is introduced for the OAuth 2.0 The following metadata parameter is introduced for the OAuth 2.0
Dynamic Client Registration Protocol [RFC7591] in support of the PKI Dynamic Client Registration Protocol [RFC7591] in support of the PKI
skipping to change at page 6, line 11 skipping to change at page 6, line 11
An [RFC4514] string representation of the expected subject An [RFC4514] string representation of the expected subject
distinguished name of the certificate the OAuth client will use in distinguished name of the certificate the OAuth client will use in
mutual TLS authentication. mutual TLS authentication.
2.2. Self-Signed Certificate Mutual TLS OAuth Client Authentication 2.2. Self-Signed Certificate Mutual TLS OAuth Client Authentication
Method Method
This method of mutual TLS OAuth client authentication is intended to This method of mutual TLS OAuth client authentication is intended to
support client authentication using self-signed certificates. As support client authentication using self-signed certificates. As
pre-requisite, the client registers an X.509 certificate or a trusted pre-requisite, the client registers an X.509 certificate or a trusted
source for its X.509 certificates (such as the "jwks_uri" as defined source for its X.509 certificates (such as the "jwks_uri" defined in
in [RFC7591]) with the authorization server. During authentication, [RFC7591] that references a JSON Web Key [RFC7517] Set containing the
TLS is utilized to validate the client's possession of the private client's certificates and public keys) with the authorization server.
key corresponding to the public key presented within the certificate During authentication, TLS is utilized to validate the client's
in the respective TLS handshake. In contrast to the PKI method, the possession of the private key corresponding to the public key
certificate chain is not validated in this case. The client is presented within the certificate in the respective TLS handshake. In
successfully authenticated, if the subject public key info of the contrast to the PKI method, the client's certificate chain is not
certificate matches the subject public key info of one of the validated by the server in this case. The client is successfully
certificates configured or registered for that particular client. authenticated if the subject public key info of the certificate
The Self-Signed Certificate method allows to use mutual TLS to matches the subject public key info of one of the certificates
authenticate clients without the need to maintain a PKI. When used configured or registered for that particular client. The Self-Signed
in conjunction with a "jwks_uri" for the client, it also allows the Certificate method allows to use mutual TLS to authenticate clients
client to rotate its X.509 certificates without the need to change without the need to maintain a PKI. When used in conjunction with a
its respective authentication data directly with the authorization "jwks_uri" for the client, it also allows the client to rotate its
server. X.509 certificates without the need to change its respective
authentication data directly with the authorization server.
2.2.1. Self-Signed Certificate Authentication Method Metadata Value 2.2.1. Self-Signed Certificate Authentication Method Metadata Value
The "OAuth Token Endpoint Authentication Methods" registry For the Self-Signed Certificate method of mutual TLS client
[IANA.OAuth.Parameters] contains values, each of which specify a authentication, this specification defines and registers the
method of authenticating a client to the authorization server. The following authentication method metadata value into the "OAuth Token
values are used to indicate supported and utilized client Endpoint Authentication Methods" registry [IANA.OAuth.Parameters].
authentication methods in authorization server metadata, such as
OpenID Connect Discovery [OpenID.Discovery] and OAuth 2.0
Authorization Server Metadata [I-D.ietf-oauth-discovery], and in the
OAuth 2.0 Dynamic Client Registration Protocol [RFC7591]. For the
Self-Signed Certificate method of binding a certificate to a client
using mutual TLS client authentication, this specification defines
and registers the following authentication method metadata value.
self_signed_tls_client_auth self_signed_tls_client_auth
Indicates that client authentication to the authorization server Indicates that client authentication to the authorization server
will occur using mutual TLS with the client utilizing a self- will occur using mutual TLS with the client utilizing a self-
signed certificate. signed certificate.
2.2.2. Client Registration Metadata 2.2.2. Client Registration Metadata
For the Self-Signed Certificate method of binding a certificate to a For the Self-Signed Certificate method of binding a certificate to a
client using mutual TLS client authentication, the existing client using mutual TLS client authentication, the existing
"jwks_uri" or "jwks" metadata parameters from [RFC7591] are used to "jwks_uri" or "jwks" metadata parameters from [RFC7591] are used to
convey the client's certificates and public keys, where the X.509 convey the client's certificates and public keys, where the X.509
certificates are represented using the JSON Web Key (JWK) [RFC7517] certificates are represented using the JSON Web Key (JWK) [RFC7517]
"x5c" parameter (note that Sec 4.7 of RFC 7517 requires that the key "x5c" parameter (note that Sec 4.7 of RFC 7517 requires that the key
in the first certificate of the "x5c" parameter must match the public in the first certificate of the "x5c" parameter must match the public
key represented by other members of the JWK). key represented by other members of the JWK).
3. Mutual TLS Sender Constrained Resources Access 3. Mutual TLS Client Certificate Bound Access Tokens
When mutual TLS is used by the client on the connection to the token When mutual TLS is used by the client on the connection to the token
endpoint, the authorization server is able to bind the issued access endpoint, the authorization server is able to bind the issued access
token to the client certificate. Such a binding is accomplished by token to the client certificate. Such a binding is accomplished by
associating the certificate with the token in a way that can be associating the certificate with the token in a way that can be
accessed by the protected resource, such as embedding the certificate accessed by the protected resource, such as embedding the certificate
hash in the issued access token directly, using the syntax described hash in the issued access token directly, using the syntax described
in Section 3.1, or through token introspection as described in in Section 3.1, or through token introspection as described in
Section 3.2. Other methods of associating a certificate with an Section 3.2. Binding the access token to the client certificate in
access token are possible, per agreement by the authorization server that fashion has the benefit of decoupling that binding from the
and the protected resource, but are beyond the scope of this client's authentication with the authorization server, which enables
specification. mutual TLS during protected resource access to serve purely as a
proof-of-possession mechanism. Other methods of associating a
certificate with an access token are possible, per agreement by the
authorization server and the protected resource, but are beyond the
scope of this specification.
The client makes protected resource requests as described in The client makes protected resource requests as described in
[RFC6750], however, those requests MUST be made over a mutually [RFC6750], however, those requests MUST be made over a mutually
authenticated TLS connection using the same certificate that was used authenticated TLS connection using the same certificate that was used
for mutual TLS at the token endpoint. for mutual TLS at the token endpoint.
The protected resource MUST obtain the client certificate used for The protected resource MUST obtain the client certificate used for
mutual TLS authentication and MUST verify that the certificate mutual TLS authentication and MUST verify that the certificate
matches the certificate associated with the access token. If they do matches the certificate associated with the access token. If they do
not match, the resource access attempt MUST be rejected with an error not match, the resource access attempt MUST be rejected with an error
per [RFC6750] using an HTTP 401 status code and the "invalid_token" per [RFC6750] using an HTTP 401 status code and the "invalid_token"
error code. error code.
Metadata to convey server and client capabilities for mutual TLS Metadata to convey server and client capabilities for mutual TLS
sender constrained access tokens is defined in Section 3.3 and client certificate bound access tokens is defined in Section 3.3 and
Section 3.4 respectively. Section 3.4 respectively.
3.1. X.509 Certificate Thumbprint Confirmation Method for JWT 3.1. X.509 Certificate Thumbprint Confirmation Method for JWT
When access tokens are represented as JSON Web Tokens (JWT)[RFC7519], When access tokens are represented as JSON Web Tokens (JWT)[RFC7519],
the certificate hash information SHOULD be represented using the the certificate hash information SHOULD be represented using the
"x5t#S256" confirmation method member defined herein. "x5t#S256" confirmation method member defined herein.
To represent the hash of a certificate in a JWT, this specification To represent the hash of a certificate in a JWT, this specification
defines the new JWT Confirmation Method RFC 7800 [RFC7800] member defines the new JWT Confirmation Method [RFC7800] member "x5t#S256"
"x5t#S256" for the X.509 Certificate SHA-256 Thumbprint. The value for the X.509 Certificate SHA-256 Thumbprint. The value of the
of the "x5t#S256" member is a base64url-encoded SHA-256[SHS] hash "x5t#S256" member is the SHA-256[SHS] hash (a.k.a. thumbprint,
(a.k.a. thumbprint or digest) of the DER encoding of the X.509 fingerprint or digest) of the DER encoding of the X.509 certificate
certificate[RFC5280] (note that certificate thumbprints are also [RFC5280] base64url-encoded [RFC4648] with with all trailing pad '='
sometimes known as certificate fingerprints). characters omitted and without the inclusion of any line breaks,
whitespace, or other additional characters.
The following is an example of a JWT payload containing an "x5t#S256" The following is an example of a JWT payload containing an "x5t#S256"
certificate thumbprint confirmation method. certificate thumbprint confirmation method.
{ {
"iss": "https://server.example.com", "iss": "https://server.example.com",
"sub": "ty.webb@example.com", "sub": "ty.webb@example.com",
"exp": 1493726400, "exp": 1493726400,
"nbf": 1493722800, "nbf": 1493722800,
"cnf":{ "cnf":{
"x5t#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2" "x5t#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
} }
} }
Figure 1: Example claims of a Certificate Thumbprint Constrained JWT Figure 1: Example JWT Claims Set with an X.509 Certificate Thumbprint
Confirmation Method
If, in the future, certificate thumbprints need to be computed using If, in the future, certificate thumbprints need to be computed using
hash functions other than SHA-256, it is suggested that additional hash functions other than SHA-256, it is suggested that additional
related JWT confirmation methods members be defined for that purpose. related JWT confirmation methods members be defined for that purpose.
For example, a new "x5t#S512" (X.509 Certificate Thumbprint using For example, a new "x5t#S512" (X.509 Certificate Thumbprint using
SHA-512) confirmation method member could be defined by registering SHA-512) confirmation method member could be defined by registering
it in the the IANA "JWT Confirmation Methods" registry it in the the IANA "JWT Confirmation Methods" registry
[IANA.JWT.Claims] for JWT "cnf" member values established by [IANA.JWT.Claims] for JWT "cnf" member values established by
[RFC7800]. [RFC7800].
3.2. Confirmation Method for Token Introspection 3.2. Confirmation Method for Token Introspection
OAuth 2.0 Token Introspection [RFC7662] defines a method for a OAuth 2.0 Token Introspection [RFC7662] defines a method for a
protected resource to query an authorization server about the active protected resource to query an authorization server about the active
state of an access token as well as to determine meta-information state of an access token as well as to determine meta-information
about the token. about the token.
For a mutual TLS sender constrained access token, the hash of the For a mutual TLS client certificate bound access token, the hash of
certificate to which the token is bound is conveyed to the protected the certificate to which the token is bound is conveyed to the
resource as meta-information in a token introspection response. The protected resource as meta-information in a token introspection
hash is conveyed using the same structure as the certificate SHA-256 response. The hash is conveyed using the same structure as the
thumbprint confirmation method, described in Section 3.1, as a top- certificate SHA-256 thumbprint confirmation method, described in
level member of the introspection response JSON. The protected Section 3.1, as a top-level member of the introspection response
resource compares that certificate hash to a hash of the client JSON. The protected resource compares that certificate hash to a
certificate used for mutual TLS authentication and rejects the hash of the client certificate used for mutual TLS authentication and
request, if they do not match. rejects the request, if they do not match.
Proof-of-Possession Key Semantics for JSON Web Tokens [RFC7800] Proof-of-Possession Key Semantics for JSON Web Tokens [RFC7800]
defined the "cnf" (confirmation) claim, which enables confirmation defined the "cnf" (confirmation) claim, which enables confirmation
key information to be carried in a JWT. However, the same proof-of- key information to be carried in a JWT. However, the same proof-of-
possession semantics are also useful for introspected access tokens possession semantics are also useful for introspected access tokens
whereby the protected resource obtains the confirmation key data as whereby the protected resource obtains the confirmation key data as
meta-information of a token introspection response and uses that meta-information of a token introspection response and uses that
information in verifying proof-of-possession. Therefore this information in verifying proof-of-possession. Therefore this
specification defines and registers proof-of-possession semantics for specification defines and registers proof-of-possession semantics for
OAuth 2.0 Token Introspection [RFC7662] using the "cnf" structure. OAuth 2.0 Token Introspection [RFC7662] using the "cnf" structure.
When included as a top-level member of an OAuth token introspection When included as a top-level member of an OAuth token introspection
response, "cnf" has the same semantics and format as the claim of the response, "cnf" has the same semantics and format as the claim of the
same name defined in [RFC7800]. While this specification only same name defined in [RFC7800]. While this specification only
explicitly uses the "x5t#S256" confirmation method member, it needed explicitly uses the "x5t#S256" confirmation method member, it needed
to define and register the higher level "cnf" structure as an to define and register the higher level "cnf" structure as an
introspection response member in order to define and use its more introspection response member in order to define and use the more
specific "x5t#S256" confirmation method. specific certificate thumbprint confirmation method.
The following is an example of an introspection response for an The following is an example of an introspection response for an
active token with an "x5t#S256" certificate thumbprint confirmation active token with an "x5t#S256" certificate thumbprint confirmation
method. method.
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
{ {
"active": true, "active": true,
"iss": "https://server.example.com", "iss": "https://server.example.com",
"sub": "ty.webb@example.com", "sub": "ty.webb@example.com",
"exp": 1493726400, "exp": 1493726400,
"nbf": 1493722800, "nbf": 1493722800,
"cnf":{ "cnf":{
"x5t#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2" "x5t#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
} }
} }
Figure 2: Example Introspection Response for a Certificate Figure 2: Example Introspection Response for a Certificate Bound
Constrained Access Token Access Token
3.3. Authorization Server Metadata 3.3. Authorization Server Metadata
This document introduces the following new authorization server This document introduces the following new authorization server
metadata parameter to signal the server's capability to issue metadata parameter to signal the server's capability to issue
certificate bound access tokens: certificate bound access tokens:
mutual_tls_sender_constrained_access_tokens tls_client_certificate_bound_access_tokens
OPTIONAL. Boolean value indicating server support for mutual TLS OPTIONAL. Boolean value indicating server support for mutual TLS
sender constrained access tokens. If omitted, the default value client certificate bound access tokens. If omitted, the default
is "false". value is "false".
3.4. Client Registration Metadata 3.4. Client Registration Metadata
The following new client metadata parameter is introduced to convey The following new client metadata parameter is introduced to convey
the client's intention to use certificate bound access tokens: the client's intention to use certificate bound access tokens:
mutual_tls_sender_constrained_access_tokens tls_client_certificate_bound_access_tokens
OPTIONAL. Boolean value used to indicate the client's intention OPTIONAL. Boolean value used to indicate the client's intention
to use mutual TLS sender constrained access tokens. If omitted, to use mutual TLS client certificate bound access tokens. If
the default value is "false". omitted, the default value is "false".
4. Implementation Considerations 4. Implementation Considerations
4.1. Authorization Server 4.1. Authorization Server
The authorization server needs to setup its TLS configuration The authorization server needs to set up its TLS configuration
appropriately for the binding methods it supports. appropriately for the binding methods it supports.
If the authorization server wants to support mutual TLS client If the authorization server wants to support mutual TLS client
authentication and other client authentication methods in parallel, authentication and other client authentication methods in parallel,
it should make mutual TLS optional. it should make mutual TLS optional.
If the authorization server supports the Self-Signed Certificate If the authorization server supports the Self-Signed Certificate
method, it should configure the TLS stack in a way that it does not method, it should configure the TLS stack in a way that it does not
verify whether the certificate presented by the client during the verify whether the certificate presented by the client during the
handshake is signed by a trusted CA certificate. handshake is signed by a trusted CA certificate.
The authorization server may also consider hosting the token The authorization server may also consider hosting the token
endpoint, and other endpoints requiring client authentication, on a endpoint, and other endpoints requiring client authentication, on a
separate host name in order to prevent unintended impact on the TLS separate host name or port in order to prevent unintended impact on
behavior of its other endpoints, e.g. authorization or registration. the TLS behavior of its other endpoints, e.g. the authorization
endpoint.
4.2. Resource Server 4.2. Resource Server
From the perspective of the resource server, TLS client Since the resource server relies on the authorization server to
authentication is used as a proof of possession method only. For the perform client authentication, there is no need for the resource
purpose of client authentication, the resource server may completely server to validate the trust chain of the client's certificate in any
rely on the authorization server. So there is no need to validate of the methods defined in this document. Mutual TLS is used only as
the trust chain of the client's certificate in any of the methods a proof-of-possession mechanism during protected resource access.
defined in this document. The resource server should therefore The resource server should therefore configure the TLS stack in a way
configure the TLS stack in a way that it does not verify whether the that it does not verify whether the certificate presented by the
certificate presented by the client during the handshake is signed by client during the handshake is signed by a trusted CA certificate.
a trusted CA certificate.
4.3. Sender Constrained Access Tokens Without Client Authentication 4.3. Certificate Bound Access Tokens Without Client Authentication
This document allows use of client authentication only or client Mutual TLS OAuth client authentication and mutual TLS client
authentication in combination with sender constraint access tokens. certificate bound access tokens can be used independently of each
Use of mutual TLS sender constrained access tokens without client other. Use of certificate bound access tokens without mutual TLS
authentication (e.g. to support binding access tokens to a TLS client OAuth client authentication, for example, is possible in support of
certificate for public clients) is also possible. The authorization binding access tokens to a TLS client certificate for public clients
server would configure the TLS stack in the same manner as for the or clients utilizing other methods of authentication to the
Self-Signed Certificate method such that it does not verify that the authorization server. The authorization server would configure the
certificate presented by the client during the handshake is signed by TLS stack in the same manner as for the Self-Signed Certificate
a trusted CA. Individual instances of a public client would then method such that it does not verify that the certificate presented by
create a self-signed certificate for mutual TLS with the the client during the handshake is signed by a trusted CA.
authorization server and resource server. The authorization server Individual instances of a client would create a self-signed
would not authenticate the client at the OAuth layer but would bind certificate for mutual TLS with both the authorization server and
issued access tokens to the certificate, which the client has proven resource server. The authorization server would not use the mutual
possession of the corresponding private key. The access token is TLS certificate to authenticate the client at the OAuth layer but
then mutual TLS sender constrained and can only be used by the client would bind the issued access token to that certificate, which the
possessing the certificate and private key and utilizing them to client has proven possession of the corresponding private key. The
negotiate mutual TLS on connections to the resource server. access token is then bound to the certificate and can only be used by
the client possessing the certificate and corresponding private key
and utilizing them to negotiate mutual TLS on connections to the
resource server.
4.4. Certificate Bound Access Tokens 4.4. Certificate Bound Access Tokens
As described in Section 3, an access token is bound to a specific As described in Section 3, an access token is bound to a specific
client certificate, which means that the same certificate must be client certificate, which means that the same certificate must be
used for mutual TLS on protected resource access. It also implies used for mutual TLS on protected resource access. It also implies
that access tokens are invalidated when a client updates the that access tokens are invalidated when a client updates the
certificate, which can be handled similar to expired access tokens certificate, which can be handled similar to expired access tokens
where the client requests a new access token (typically with a where the client requests a new access token (typically with a
refresh token) and retries the protected resource request. refresh token) and retries the protected resource request.
4.5. Implicit Grant Unsupported 4.5. Implicit Grant Unsupported
This document describes binding an access token to the client This document describes binding an access token to the client
certificate presented on the TLS connection from the client to the certificate presented on the TLS connection from the client to the
authorization server's token endpoint, however, certificate binding authorization server's token endpoint, however, such binding of
of access tokens issued directly from the authorization endpoint via access tokens issued directly from the authorization endpoint via the
the implicit grant flow is explicitly out of scope. End users implicit grant flow is explicitly out of scope. End users interact
interact directly with the authorization endpoint using a web browser directly with the authorization endpoint using a web browser and the
and the use of client certificates in user's browsers bring use of client certificates in user's browsers bring operational and
operational and usability issues, which make it undesirable to usability issues, which make it undesirable to support certificate
support certificate bound access tokens issued in the implicit grant bound access tokens issued in the implicit grant flow.
flow. Implementations wanting to employ certificate bound sender Implementations wanting to employ certificate bound access tokens
constrained access tokens should utilize grant types that involve the should utilize grant types that involve the client making an access
client making an access token request directly to the token endpoint token request directly to the token endpoint (e.g. the authorization
(e.g. the authorization code and refresh token grant types). code and refresh token grant types).
4.6. TLS Termination
An authorization server or resource server MAY choose to terminate
TLS connections at a load balancer, reverse proxy, or other network
intermediary. How the client certificate metadata is securely
communicated between the intermediary and the application server in
this case is out of scope of this specification.
5. Security Considerations 5. Security Considerations
5.1. TLS Versions and Best Practices 5.1. TLS Versions and Best Practices
TLS 1.2 [RFC5246] is cited in this document because, at the time of TLS 1.2 [RFC5246] is cited in this document because, at the time of
writing, it is the latest version that is widely deployed. However, writing, it is the latest version that is widely deployed. However,
this document is applicable with other TLS versions supporting this document is applicable with other TLS versions supporting
certificate-based client authentication. Implementation security certificate-based client authentication. Implementation security
considerations for TLS, including version recommendations, can be considerations for TLS, including version recommendations, can be
skipping to change at page 12, line 19 skipping to change at page 12, line 39
DN but issued by a different CA, which the authorization server DN but issued by a different CA, which the authorization server
trusts. To cope with that threat, the authorization server should trusts. To cope with that threat, the authorization server should
only accept as trust anchors a limited number of CAs whose only accept as trust anchors a limited number of CAs whose
certificate issuance policy meets its security requirements. There certificate issuance policy meets its security requirements. There
is an assumption then that the client and server agree on the set of is an assumption then that the client and server agree on the set of
trust anchors that the server uses to create and validate the trust anchors that the server uses to create and validate the
certificate chain. Without this assumption the use of a Subject DN certificate chain. Without this assumption the use of a Subject DN
to identify the client certificate would open the server up to to identify the client certificate would open the server up to
certificate spoofing attacks. certificate spoofing attacks.
5.3. X.509 Certificate Parsing and Validation Complexity
Parsing and validation of X.509 certificates and certificate chains
is complex and implementation mistakes have previously exposed
security vulnerabilities. Complexities of validation include (but
are not limited to) [X509Pitfalls] [DangerousCode] [RFC5280]:
o checking of Basic Constraints, basic and extended Key Usage
constraints, validity periods, and critical extensions;
o handling of null-terminator bytes and non-canonical string
representations in subject names;
o handling of wildcard patterns in subject names;
o recursive verification of certificate chains and checking
certificate revocation.
For these reasons, implementors SHOULD use an established and well-
tested X.509 library (such as one used by an established TLS library)
for validation of X.509 certificate chains and SHOULD NOT attempt to
write their own X.509 certificate validation procedures.
6. IANA Considerations 6. IANA Considerations
6.1. JWT Confirmation Methods Registration 6.1. JWT Confirmation Methods Registration
This specification requests registration of the following value in This specification requests registration of the following value in
the IANA "JWT Confirmation Methods" registry [IANA.JWT.Claims] for the IANA "JWT Confirmation Methods" registry [IANA.JWT.Claims] for
JWT "cnf" member values established by [RFC7800]. JWT "cnf" member values established by [RFC7800].
o Confirmation Method Value: "x5t#S256" o Confirmation Method Value: "x5t#S256"
o Confirmation Method Description: X.509 Certificate SHA-256 o Confirmation Method Description: X.509 Certificate SHA-256
Thumbprint Thumbprint
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.1 of [[ this specification ]] o Specification Document(s): Section 3.1 of [[ this specification ]]
6.2. OAuth Authorization Server Metadata Registration 6.2. OAuth Authorization Server Metadata Registration
This specification requests registration of the following value in This specification requests registration of the following value in
the IANA "OAuth Authorization Server Metadata" registry the IANA "OAuth Authorization Server Metadata" registry
[IANA.OAuth.Parameters] established by [I-D.ietf-oauth-discovery]. [IANA.OAuth.Parameters] established by [I-D.ietf-oauth-discovery].
o Metadata Name: "mutual_tls_sender_constrained_access_tokens" o Metadata Name: "tls_client_certificate_bound_access_tokens"
o Metadata Description: Indicates authorization server support for o Metadata Description: Indicates authorization server support for
mutual TLS sender constrained access tokens. mutual TLS client certificate bound access tokens.
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.3 of [[ this specification ]] o Specification Document(s): Section 3.3 of [[ this specification ]]
6.3. Token Endpoint Authentication Method Registration 6.3. Token Endpoint Authentication Method Registration
This specification requests registration of the following value in This specification requests registration of the following value in
the IANA "OAuth Token Endpoint Authentication Methods" registry the IANA "OAuth Token Endpoint Authentication Methods" registry
[IANA.OAuth.Parameters] established by [RFC7591]. [IANA.OAuth.Parameters] established by [RFC7591].
o Token Endpoint Authentication Method Name: "tls_client_auth" o Token Endpoint Authentication Method Name: "tls_client_auth"
skipping to change at page 13, line 30 skipping to change at page 14, line 24
o Claim Description: Confirmation o Claim Description: Confirmation
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.2 of [[ this specification ]] o Specification Document(s): Section 3.2 of [[ this specification ]]
6.5. OAuth Dynamic Client Registration Metadata Registration 6.5. OAuth Dynamic Client Registration Metadata Registration
This specification requests registration of the following client This specification requests registration of the following client
metadata definitions in the IANA "OAuth Dynamic Client Registration metadata definitions in the IANA "OAuth Dynamic Client Registration
Metadata" registry [IANA.OAuth.Parameters] established by [RFC7591]: Metadata" registry [IANA.OAuth.Parameters] established by [RFC7591]:
o Client Metadata Name: o Client Metadata Name: "tls_client_certificate_bound_access_tokens"
"mutual_tls_sender_constrained_access_tokens"
o Client Metadata Description: Indicates the client's intention to o Client Metadata Description: Indicates the client's intention to
use mutual TLS sender constrained access tokens. use mutual TLS client certificate bound access tokens.
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.4 of [[ this specification ]] o Specification Document(s): Section 3.4 of [[ this specification ]]
o Client Metadata Name: "tls_client_auth_subject_dn" o Client Metadata Name: "tls_client_auth_subject_dn"
o Client Metadata Description: String value specifying the expected o Client Metadata Description: String value specifying the expected
subject distinguished name of the client certificate. subject distinguished name of the client certificate.
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 2.1.2 of [[ this specification o Specification Document(s): Section 2.1.2 of [[ this specification
]] ]]
skipping to change at page 14, line 21 skipping to change at page 15, line 10
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access Protocol [RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access Protocol
(LDAP): String Representation of Distinguished Names", (LDAP): String Representation of Distinguished Names",
RFC 4514, DOI 10.17487/RFC4514, June 2006, RFC 4514, DOI 10.17487/RFC4514, June 2006,
<https://www.rfc-editor.org/info/rfc4514>. <https://www.rfc-editor.org/info/rfc4514>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
skipping to change at page 15, line 7 skipping to change at page 15, line 46
RFC 7800, DOI 10.17487/RFC7800, April 2016, RFC 7800, DOI 10.17487/RFC7800, April 2016,
<https://www.rfc-editor.org/info/rfc7800>. <https://www.rfc-editor.org/info/rfc7800>.
[SHS] National Institute of Standards and Technology, "Secure [SHS] National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, March 2012, Hash Standard (SHS)", FIPS PUB 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/ <http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>. fips-180-4.pdf>.
7.2. Informative References 7.2. Informative References
[DangerousCode]
Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., Boneh,
D., and V. Shmatikov, "The Most Dangerous Code in the
World: Validating SSL Certificates in Non-Browser
Software",
<http://www.cs.utexas.edu/~shmat/shmat_ccs12.pdf>.
[I-D.ietf-oauth-discovery] [I-D.ietf-oauth-discovery]
Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", draft-ietf-oauth- Authorization Server Metadata", draft-ietf-oauth-
discovery-08 (work in progress), November 2017. discovery-10 (work in progress), March 2018.
[I-D.ietf-oauth-token-binding] [I-D.ietf-oauth-token-binding]
Jones, M., Campbell, B., Bradley, J., and W. Denniss, Jones, M., Campbell, B., Bradley, J., and W. Denniss,
"OAuth 2.0 Token Binding", draft-ietf-oauth-token- "OAuth 2.0 Token Binding", draft-ietf-oauth-token-
binding-05 (work in progress), October 2017. binding-06 (work in progress), March 2018.
[IANA.JWT.Claims] [IANA.JWT.Claims]
IANA, "JSON Web Token Claims", IANA, "JSON Web Token Claims",
<http://www.iana.org/assignments/jwt>. <http://www.iana.org/assignments/jwt>.
[IANA.OAuth.Parameters] [IANA.OAuth.Parameters]
IANA, "OAuth Parameters", IANA, "OAuth Parameters",
<http://www.iana.org/assignments/oauth-parameters>. <http://www.iana.org/assignments/oauth-parameters>.
[OpenID.Discovery] [RFC4517] Legg, S., Ed., "Lightweight Directory Access Protocol
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID (LDAP): Syntaxes and Matching Rules", RFC 4517,
Connect Discovery 1.0", August 2015, DOI 10.17487/RFC4517, June 2006,
<http://openid.net/specs/ <https://www.rfc-editor.org/info/rfc4517>.
openid-connect-discovery-1_0.html>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth [RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009, 2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
August 2013, <https://www.rfc-editor.org/info/rfc7009>. August 2013, <https://www.rfc-editor.org/info/rfc7009>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015, DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>. <https://www.rfc-editor.org/info/rfc7517>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
skipping to change at page 16, line 9 skipping to change at page 17, line 5
<https://www.rfc-editor.org/info/rfc7591>. <https://www.rfc-editor.org/info/rfc7591>.
[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015, RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>. <https://www.rfc-editor.org/info/rfc7662>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[X509Pitfalls]
Wong, D., "Common x509 certificate validation/creation
pitfalls", September 2016,
<https://www.cryptologie.net/article/374/
common-x509-certificate-validationcreation-pitfalls>.
Appendix A. Relationship to Token Binding Appendix A. Relationship to Token Binding
OAuth 2.0 Token Binding [I-D.ietf-oauth-token-binding] enables the OAuth 2.0 Token Binding [I-D.ietf-oauth-token-binding] enables the
application of Token Binding to the various artifacts and tokens application of Token Binding to the various artifacts and tokens
employed throughout OAuth. That includes binding of an access token employed throughout OAuth. That includes binding of an access token
to a Token Binding key, which bears some similarities in motivation to a Token Binding key, which bears some similarities in motivation
and design to the mutual TLS sender constrained resources access and design to the mutual TLS client certificate bound access tokens
defined in this document. Both documents define what is often called defined in this document. Both documents define what is often called
a proof-of-possession security mechanism for access tokens, whereby a a proof-of-possession security mechanism for access tokens, whereby a
client must demonstrate possession of cryptographic keying material client must demonstrate possession of cryptographic keying material
when accessing a protected resource. The details differ somewhat when accessing a protected resource. The details differ somewhat
between the two documents but both have the authorization server bind between the two documents but both have the authorization server bind
the access token it issues to an asymmetric key pair on the client. the access token that it issues to an asymmetric key pair held by the
The client then proves possession of the private key from that pair client. The client then proves possession of the private key from
on the TLS connection over which the protected resource is accessed. that pair with respect to the TLS connection over which the protected
resource is accessed.
The two documents then are effectively competing specifications, at Token Binding uses bare keys that are generated on the client, which
least with respect to the binding of access tokens. Token Binding avoids many of the difficulties of creating, distributing, and
uses bare keys that are generated on the client, which avoids many of managing certificates used in this specification. However, at the
the difficulties of creating, distributing, and managing certificates time of writing, Token Binding is fairly new and there is relatively
and has the potential to see wider scale adoption and deployment. little support for it in available application development platforms
However, at the time of writing, Token Binding is fairly new and and tooling. Until better support for the underlying core Token
there is relatively little support for it in available application Binding specifications exists, practical implementations of OAuth 2.0
development platforms and tooling. Until better support for the Token Binding are infeasible. Mutual TLS, on the other hand, has
underlying core Token Binding specifications exists, practical been around for some time and enjoys widespread support in web
implementations of OAuth 2.0 Token Binding are infeasible. Despite servers and development platforms. As a consequence, OAuth 2.0
its name, Token Binding doesn't have a monopoly on the binding of Mutual TLS Client Authentication and Certificate Bound Access Tokens
tokens. Mutual TLS, on the other hand, has been around for some time can be built and deployed now using existing platforms and tools. In
and enjoys widespread support in web servers and development the future, the two specifications are likely to be deployed in
platforms. Mutual TLS for OAuth 2.0 can be built and deployed now parallel for solving similar problems in different environments.
using existing platforms and tools. There are emerging and immediate Authorization servers may even support both specifications
scenarios, such as OAuth enabled financial transactions motivated by simultaneously using different proof-of-possession mechanisms for
regulatory requirements in some cases, which demand the additional tokens issued to different clients.
security protections of proof-of-possession access tokens. This
document aspires to provide standardized and expeditious solution for
those scenarios.
Appendix B. Acknowledgements Appendix B. Acknowledgements
Scott "not Tomlinson" Tomilson and Matt Peterson were involved in Scott "not Tomlinson" Tomilson and Matt Peterson were involved in
design and development work on a mutual TLS OAuth client design and development work on a mutual TLS OAuth client
authentication implementation that informed some of the content of authentication implementation, which predates this document.
this document. Experience and learning from that work informed some of the content
of this document.
Additionally, the authors would like to thank the following people Additionally, the authors would like to thank the following people
for their input and contributions to the specification: Sergey for their input and contributions to the specification: Sergey
Beryozkin, Vladimir Dzhuvinov, Samuel Erdtman, Leif Johansson, Phil Beryozkin, Vladimir Dzhuvinov, Samuel Erdtman, Leif Johansson,
Hunt, Takahiko Kawasaki, Sean Leonard, Kepeng Li, James Manger, Jim Michael Jones, Phil Hunt, Benjamin Kaduk, Takahiko Kawasaki, Sean
Manico, Nov Matake, Sascha Preibisch, Justin Richer, Dave Tonge, and Leonard, Kepeng Li, Neil Madden, James Manger, Jim Manico, Nov
Hannes Tschofenig. Matake, Sascha Preibisch, Justin Richer, Dave Tonge, and Hannes
Tschofenig.
Appendix C. Document(s) History Appendix C. Document(s) History
[[ to be removed by the RFC Editor before publication as an RFC ]] [[ to be removed by the RFC Editor before publication as an RFC ]]
draft-ietf-oauth-mtls-08
o Incorporate clarifications and editorial improvements from Justin
Richer's WGLC review
o Drop the use of the "sender constrained" terminology per WGLC
feedback from Neil Madden (including changing the metadata
parameters from mutual_tls_sender_constrained_access_tokens to
tls_client_certificate_bound_access_tokens)
o Add a new security considerations section on X.509 parsing and
validation per WGLC feedback from Neil Madden and Benjamin Kaduk
o Note that a server can terminate TLS at a load balancer, reverse
proxy, etc. but how the client certificate metadata is securely
communicated to the backend is out of scope per WGLC feedback
o Note that revocation checking is at the discretion of the AS per
WGLC feedback
o Editorial updates and clarifications
o Update draft-ietf-oauth-discovery reference to -10 and draft-ietf-
oauth-token-binding to -06
o Add folks involved in WGLC feedback to the acknowledgements list
draft-ietf-oauth-mtls-07 draft-ietf-oauth-mtls-07
o Update to use the boilerplate from RFC 8174 o Update to use the boilerplate from RFC 8174
draft-ietf-oauth-mtls-06 draft-ietf-oauth-mtls-06
o Add an appendix section describing the relationship of this o Add an appendix section describing the relationship of this
document to OAuth Token Binding as requested during the the document to OAuth Token Binding as requested during the the
Singapore meeting https://datatracker.ietf.org/doc/minutes- Singapore meeting https://datatracker.ietf.org/doc/minutes-
100-oauth/ 100-oauth/
 End of changes. 60 change blocks. 
228 lines changed or deleted 298 lines changed or added

This html diff was produced by rfcdiff 1.46. The latest version is available from http://tools.ietf.org/tools/rfcdiff/