draft-ietf-oauth-mtls-03.txt   draft-ietf-oauth-mtls-04.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: January 28, 2018 Yubico Expires: April 14, 2018 Yubico
N. Sakimura N. Sakimura
Nomura Research Institute Nomura Research Institute
T. Lodderstedt T. Lodderstedt
YES Europe AG YES Europe AG
July 27, 2017 October 11, 2017
Mutual TLS Profile for OAuth 2.0 Mutual TLS Profile for OAuth 2.0
draft-ietf-oauth-mtls-03 draft-ietf-oauth-mtls-04
Abstract Abstract
This document describes Transport Layer Security (TLS) mutual This document describes Transport Layer Security (TLS) mutual
authentication using X.509 certificates as a mechanism for OAuth authentication using X.509 certificates as a mechanism for OAuth
client authentication to the token endpoint as well as for client authentication to the authorization sever as well as for
certificate bound sender constrained access tokens. certificate bound sender constrained access tokens.
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 http://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 January 28, 2018. This Internet-Draft will expire on April 14, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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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 . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Mutual TLS for Client Authentication . . . . . . . . . . . . 4 2. Mutual TLS for OAuth Client Authentication . . . . . . . . . 4
2.1. Mutual TLS Client Authentication to the Token Endpoint . 4 2.1. PKI Mutual TLS OAuth Client Authentication Method . . . . 4
2.2. Authorization Server Metadata . . . . . . . . . . . . . . 5 2.1.1. PKI Authentication Method Metadata Value . . . . . . 5
2.3. Dynamic Client Registration . . . . . . . . . . . . . . . 5 2.1.2. Client Registration Metadata . . . . . . . . . . . . 5
2.2. Self-Signed Certificate Mutual TLS OAuth Client
Authentication Method . . . . . . . . . . . . . . . . . . 5
2.2.1. Self-Signed Certificate Authentication Method
Metadata Value . . . . . . . . . . . . . . . . . . . 6
2.2.2. Client Registration Metadata . . . . . . . . . . . . 6
3. Mutual TLS Sender Constrained Resources Access . . . . . . . 6 3. Mutual TLS Sender Constrained Resources Access . . . . . . . 6
3.1. X.509 Certificate SHA-256 Thumbprint Confirmation Method 3.1. X.509 Certificate Thumbprint Confirmation Method for JWT 7
for JWT . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Confirmation Method for Token Introspection . . . . . . . 8 3.2. Confirmation Method for Token Introspection . . . . . . . 8
4. Implementation Considerations . . . . . . . . . . . . . . . . 9 3.3. Authorization Server Metadata . . . . . . . . . . . . . . 9
4.1. Authorization Server . . . . . . . . . . . . . . . . . . 9 3.4. Client Registration Metadata . . . . . . . . . . . . . . 9
4.2. Resource Server . . . . . . . . . . . . . . . . . . . . . 9 4. Implementation Considerations . . . . . . . . . . . . . . . . 10
4.1. Authorization Server . . . . . . . . . . . . . . . . . . 10
4.2. Resource Server . . . . . . . . . . . . . . . . . . . . . 10
4.3. Sender Constrained Access Tokens Without Client 4.3. Sender Constrained Access Tokens Without Client
Authentication . . . . . . . . . . . . . . . . . . . . . 10 Authentication . . . . . . . . . . . . . . . . . . . . . 10
4.4. Certificate Bound Access Tokens . . . . . . . . . . . . . 10 4.4. Certificate Bound Access Tokens . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5.1. JWT Confirmation Methods Registration . . . . . . . . . . 10 5.1. JWT Confirmation Methods Registration . . . . . . . . . . 11
5.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 10
5.2. OAuth Authorization Server Metadata Registration . . . . 11 5.2. OAuth Authorization Server Metadata Registration . . . . 11
5.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 11 5.3. Token Endpoint Authentication Method Registration . . . . 12
5.3. Token Endpoint Authentication Method Registration . . . . 11 5.4. OAuth Token Introspection Response Registration . . . . . 12
5.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 11
5.4. OAuth Token Introspection Response Registration . . . . . 11
5.4.1. Registry Contents . . . . . . . . . . . . . . . . . . 11
5.5. OAuth Dynamic Client Registration Metadata Registration . 12 5.5. OAuth Dynamic Client Registration Metadata Registration . 12
5.5.1. Registry Contents . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6.1. TLS Versions and Best Practices . . . . . . . . . . . . . 13
6.1. TLS Versions and Best Practices . . . . . . . . . . . . . 12 6.2. X.509 Certificate Spoofing . . . . . . . . . . . . . . . 13
6.2. X.509 Certificate Spoofing . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 14 7.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 15 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 15
Appendix B. Document(s) History . . . . . . . . . . . . . . . . 15 Appendix B. Document(s) History . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
This document describes Transport Layer Security (TLS) mutual This document describes Transport Layer Security (TLS) mutual
authentication using X.509 certificates as a mechanism for OAuth authentication using X.509 certificates as a mechanism for OAuth
client authentication to the token endpoint as well as for sender client authentication to the authorization sever as well as for
constrained access to OAuth protected resources. sender constrained access to OAuth protected resources.
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 with the authorization server's token endpoint. when interacting directly with the authorization server. This
This document describes an additional mechanism of client document describes an additional mechanism of client authentication
authentication utilizing mutual TLS [RFC5246] certificate-based utilizing mutual TLS [RFC5246] certificate-based authentication,
authentication, which provides better security characteristics than which provides better security characteristics than shared secrets.
shared secrets. While [RFC6749] documents client authentication for requests to the
token endpoint, extensions to OAuth 2.0 (such as Introspection
[RFC7662] and Revocation [RFC7009]) define endpoints that also
utilize client authentication and the mutual TLS methods defined
herein are applicable to those endpoints as well.
Mutual TLS sender constrained access to protected resources ensures Mutual TLS sender constrained access to protected resources ensures
that only the party in possession of the private key corresponding to that only the party in possession of the private key corresponding to
the certificate can utilize the access token to get access to the the certificate can utilize the access token to get access to the
associated resources. Such a constraint is unlike the case of the associated resources. Such a constraint is unlike the case of the
basic bearer token described in [RFC6750], where any party in basic bearer token described in [RFC6750], where any party in
possession of the access token can use it to access the associated possession of the access token can use it to access the associated
resources. Mutual TLS sender constrained access binds the access resources. Mutual TLS sender constrained access binds the access
token to the client's certificate thus preventing the use of stolen token to the client's certificate thus preventing the use of stolen
access tokens or replay of access tokens by unauthorized parties. access tokens or replay of access tokens by unauthorized parties.
Mutual TLS sender constrained access tokens and mutual TLS client Mutual TLS sender constrained access tokens and mutual TLS client
authentication are distinct mechanisms that don't necessarily need to authentication are distinct mechanisms, which are complementary but
be deployed together. don't necessarily need to be deployed 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 RFC "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
1.2. Terminology 1.2. Terminology
This specification uses the following phrases interchangeably: This specification uses the following phrases interchangeably:
Transport Layer Security (TLS) Mutual Authentication Transport Layer Security (TLS) Mutual Authentication
Mutual TLS Mutual TLS
These phrases all refer to the process whereby a client uses it's These phrases all refer to the process whereby a client presents its
X.509 certificate to authenticate itself with a server when X.509 certificate and proves possession of the corresponding private
negotiating a TLS session. In TLS 1.2 [RFC5246] this requires the key to a server when negotiating a TLS session. In TLS 1.2 [RFC5246]
client to send Client Certificate and Certificate Verify messages this requires the client to send Client Certificate and Certificate
during the TLS handshake and for the server to verify these messages. Verify messages during the TLS handshake and for the server to verify
these messages.
2. Mutual TLS for Client Authentication
2.1. Mutual TLS Client Authentication to the Token Endpoint 2. Mutual TLS for OAuth Client Authentication
The following section defines, as an extension of OAuth 2.0, This section defines, as an extension of OAuth 2.0, Section 2.3
Section 2.3 [RFC6749], the use of 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 authentications is determined by the authorization server for client authentications 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 or statically
configured or otherwise established). OAuth 2.0 requires that access configured or otherwise established).
token requests by the client to the token endpoint use TLS. In order
to utilize TLS for client authentication, the TLS connection MUST In order to utilize TLS for OAuth client authentication, the TLS
have been established or reestablished with mutual X.509 certificate connection between the client and the authorization server MUST have
been established or reestablished with mutual 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 access token requests to the token endpoint, regardless of For all requests to the authorization server utilizing mutual TLS
the grant type used, 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 and allows for trust models to vary as appropriate of the certificate. The authorization server can locate the client
for a given deployment. The authorization server can locate the configuration using the client identifier and check the certificate
client configuration by the client identifier and check the presented in the TLS Handshake against the expected credentials for
certificate presented in the TLS Handshake against the expected that client. The authorization server MUST enforce some method of
credentials for that client. The authorization server MUST enforce binding a certificate to a client. Sections Section 2.1 and
some method of binding a certificate to a client. The following two Section 2.2 below define two ways of binding a certificate to a
binding methods are defined: client as two distinct client authentication methods.
PKI The PKI method uses a distinguished name (DN) to identify the
client. The TLS handshake is utilized to validate the client's
possession of the private key corresponding to the public key in
the certificate and to validate the corresponding certificate
chain. The client is successfully authenticated if the subject
information in the certificate matches the configured DN. The
client may prescribe the DN of the issuer of its certificates.
The authorization server will enforce this restriction after the
TLS handshake took place. Setting the issuer to a certain CA
securely scopes the DN of the client to this CA and shall prevent
an attacker from impersonating a client by using a certificate for
the client's DN obtained from a different CA. The PKI 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.
Public Key The Public Key method uses public keys to identify
clients. As pre-requisite, the client registers a X.509
certificate or a trusted source for its X.509 certificates (jwks
uri as defined in [RFC7591]) with the authorization server.
During authentication, TLS is utilized to validate the client's
possession of the private key corresponding to the public key
presented in the respective TLS handshake. In contrast to the PKI
method, the certificate chain is not validated in this case. The
client is successfully authenticated, if the subject public key
info of the validated certificate matches the subject public key
info of one the certificates configured for that particular
client. The Public Key method allows to use mutual TLS to
authenticate clients without the need to maintain a PKI. When
used in conjunction with a trusted X.509 certificate source, it
also allows the client to rotate its X.509 certificates without
the need to change its respective authentication data at the
authorization server.
2.2. Authorization Server Metadata
In authorization server metadata, such as [OpenID.Discovery] and 2.1. PKI Mutual TLS OAuth Client Authentication Method
[I-D.ietf-oauth-discovery], the
"token_endpoint_auth_methods_supported" parameter indicates client
authentication methods to the token endpoint supported by the
authorization server. This document introduces the value
"tls_client_auth" for use in "token_endpoint_auth_methods_supported"
to indicate server support for mutual TLS client authentication
utilizing the PKI method. And for the support of mutual TLS client
authentication utilizing the Public Key method, the value
"pub_key_tls_client_auth" is used in
"token_endpoint_auth_methods_supported".
This document also introduces a new authorization server metadata The PKI (public key infrastructure) method of mutual TLS OAuth client
parameter: authentication uses a subject distinguished name (DN) and validated
certificate chain to identify the client. The TLS handshake is
utilized to validate the client's possession of the private key
corresponding to the public key in the certificate and to validate
the corresponding certificate chain. The client is successfully
authenticated if the subject information in the certificate matches
the expected DN configured or registered for that particular client.
The PKI 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).
mutual_tls_sender_constrained_access_tokens 2.1.1. PKI Authentication Method Metadata Value
OPTIONAL. Boolean value indicating server support for mutual TLS
sender constrained access tokens. If omitted, the default value
is "false".
2.3. Dynamic Client Registration The "OAuth Token Endpoint Authentication Methods" registry
[IANA.OAuth.Parameters] contains values, each of which specify a
method of authenticating a client to the authorization server. The
values are used to indicated supported and utilized client
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.
This document adds the following values and metadata parameters to tls_client_auth
OAuth 2.0 Dynamic Client Registration [RFC7591]. Indicates that client authentication to the authorization server
will occur with mutual TLS utilizing the PKI method of associating
a certificate to a client.
The client metadata parameter 2.1.2. Client Registration Metadata
"mutual_tls_sender_constrained_access_tokens" is a Boolean value used
to indicate the client's intention to use mutual TLS sender
constrained access tokens. If omitted, the default value is "false".
For the PKI method of binding a certificate to a client, the value The following metadata parameter is introduced for the OAuth 2.0
"tls_client_auth" is used to indicate the client's intention to use Dynamic Client Registration Protocol [RFC7591] in support of the PKI
mutual TLS as an authentication method to the token endpoint for the method of binding a certificate to a client:
"token_endpoint_auth_method" client metadata parameter. And the
following two metadata parameters are introduced in support of the
PKI method of binding a certificate to a client:
tls_client_auth_subject_dn tls_client_auth_subject_dn
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.
tls_client_auth_root_dn 2.2. Self-Signed Certificate Mutual TLS OAuth Client Authentication
OPTIONAL. An [RFC4514] string representation of a distinguished Method
name that can optionally be used to constrain, for the given
client, the expected distinguished name of the root issuer of the
client certificate.
With the Public Key method of binding a certificate to a client, the This method of mutual TLS OAuth client authentication is intended to
value "pub_key_tls_client_auth" is used for the support client authentication using self-signed certificates. As
"token_endpoint_auth_method" client metadata parameter to indicate pre-requisite, the client registers a X.509 certificate or a trusted
the client's intention to use mutual TLS with a self-signed source for its X.509 certificates (such as the "jwks_uri" as defined
certificate as an authentication method. For the Public Key method, in [RFC7591]) with the authorization server. During authentication,
the existing "jwks_uri" or "jwks" metadata parameters from [RFC7591] TLS is utilized to validate the client's possession of the private
are used to convey client's public keys, where the X.509 certificates key corresponding to the public key presented within the certificate
are represented using the "x5c" parameter from [RFC7517]. in the respective TLS handshake. In contrast to the PKI method, the
certificate chain is not validated in this case. The client is
successfully authenticated, if the subject public key info of the
certificate matches the subject public key info of one the
certificates configured or registered for that particular client.
The Self-Signed Certificate method allows to use mutual TLS to
authenticate clients without the need to maintain a PKI. When used
in conjunction with a "jwks_uri" for the client, it also allows the
client to rotate its X.509 certificates without the need to change
its respective authentication data directly with at the authorization
server.
2.2.1. Self-Signed Certificate Authentication Method Metadata Value
The "OAuth Token Endpoint Authentication Methods" registry
[IANA.OAuth.Parameters] contains values, each of which specify a
method of authenticating a client to the authorization server. The
values are used to indicated supported and utilized client
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
Indicates that client authentication to the authorization server
will occur using mutual TLS with the client utilizing a self-
signed certificate.
2.2.2. Client Registration Metadata
For the Self-Signed Certificate method of binding a certificate to a
client using mutual TLS client authentication, the existing
"jwks_uri" or "jwks" metadata parameters from [RFC7591] are used to
convey client's certificates and public keys, where the X.509
certificates are represented using the JSON Web Key (JWK) [RFC7517]
"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
key represented by other members of the JWK).
3. Mutual TLS Sender Constrained Resources Access 3. Mutual TLS Sender Constrained Resources Access
When mutual TLS is used at the token endpoint, the authorization When mutual TLS is used at the token endpoint, the authorization
server is able to bind the issued access token to the client server is able to bind the issued access token to the client
certificate. Such a binding is accomplished by associating the certificate. Such a binding is accomplished by associating the
certificate with the token in a way that can be accessed by the certificate with the token in a way that can be accessed by the
protected resource, such as embedding the certificate hash in the protected resource, such as embedding the certificate hash in the
issued access token directly, using the syntax described in issued access token directly, using the syntax described in
Section 3.1, or through token introspection as described in Section 3.1, or through token introspection as described in
skipping to change at page 7, line 14 skipping to change at page 7, line 21
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.
3.1. X.509 Certificate SHA-256 Thumbprint Confirmation Method for JWT Metadata to convey server and client capabilities for mutual TLS
sender constrained access tokens is defined in Section 3.3 and
Section 3.4 respectively.
3.1. X.509 Certificate Thumbprint Confirmation Method for JWT
When access tokens are represented as a JSON Web Tokens When access tokens are represented as a JSON Web Tokens
(JWT)[RFC7519], the certificate hash information SHOULD be (JWT)[RFC7519], the certificate hash information SHOULD be
represented using the "x5t#S256" confirmation method member defined represented using the "x5t#S256" confirmation method member defined
herein. 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 RFC 7800 [RFC7800] member
"x5t#S256" for the X.509 Certificate SHA-256 Thumbprint. The value "x5t#S256" for the X.509 Certificate SHA-256 Thumbprint. The value
of the "x5t#S256" member is a base64url-encoded SHA-256[SHS] hash of the "x5t#S256" member is a base64url-encoded SHA-256[SHS] hash
skipping to change at page 8, line 15 skipping to change at page 8, line 36
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 sender constrained access token, the hash of the
certificate to which the token is bound is conveyed to the protected certificate to which the token is bound is conveyed to the protected
resource as meta-information in a token introspection response. The resource as meta-information in a token introspection response. The
hash is conveyed using same structure as the certificate SHA-256 hash is conveyed using the same structure as the certificate SHA-256
thumbprint confirmation method, described in Section 3.1, as a top- thumbprint confirmation method, described in Section 3.1, as a top-
level member of the introspection response JSON. The protected level member of the introspection response JSON. The protected
resource compares that certificate hash to a hash of the client resource compares that certificate hash to a hash of the client
certificate used for mutual TLS authentication and rejects the certificate used for mutual TLS authentication and rejects the
request, if they do not match. 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
skipping to change at page 9, line 22 skipping to change at page 9, line 32
"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
Constrained Access Token Constrained Access Token
3.3. Authorization Server Metadata
This document introduces the following new authorization server
metadata parameter to signal the server's capability to issue
certificate bound access tokens:
mutual_tls_sender_constrained_access_tokens
OPTIONAL. Boolean value indicating server support for mutual TLS
sender constrained access tokens. If omitted, the default value
is "false".
3.4. Client Registration Metadata
The following new client metadata parameter is introduced to convey
the client's intention to use certificate bound access tokens:
mutual_tls_sender_constrained_access_tokens
OPTIONAL. Boolean value used to indicate the client's intention
to use mutual TLS sender constrained access tokens. If 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 setup 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 on the token endpoint. it should make mutual TLS optional.
If the authorization server supports the Public Key method, it should
configure the TLS stack in a way that it does not verify whether the
certificate presented by the client during the handshake is signed by
a trusted CA certificate.
Please note: the Public Key method is intended to support client If the authorization server supports the Self-Signed Certificate
authentication using self-signed certificates. method, it should configure the TLS stack in a way that it does not
verify whether the certificate presented by the client during the
handshake is signed by a trusted CA certificate.
The authorization server may also consider hosting the token endpoint The authorization server may also consider hosting the token
on a separate host name in order to prevent unintended impact on the endpoint, and other endpoints requiring client authentication, on a
TLS behavior of its other endpoints, e.g. authorization or separate host name in order to prevent unintended impact on the TLS
registration. behavior of its other endpoints, e.g. authorization or registration.
4.2. Resource Server 4.2. Resource Server
From the perspective of the resource server, TLS client From the perspective of the resource server, TLS client
authentication is used as a proof of possession method only. For the authentication is used as a proof of possession method only. For the
purpose of client authentication, the resource server may completely purpose of client authentication, the resource server may completely
rely on the authorization server. So there is no need to validate rely on the authorization server. So there is no need to validate
the trust chain of the client's certificate in any of the methods the trust chain of the client's certificate in any of the methods
defined in this document. The resource server should therefore defined in this document. The resource server should therefore
configure the TLS stack in a way that it does not verify whether the configure the TLS stack in a way that it does not verify whether the
certificate presented by the client during the handshake is signed by certificate presented by the 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. Sender Constrained Access Tokens Without Client Authentication
This document allows for the use of client authentication only or This document allows for the use of client authentication only or
client authentication in combination with sender constraint access client authentication in combination with sender constraint access
tokens. Use of mutual TLS sender constrained access tokens without tokens. Use of mutual TLS sender constrained access tokens without
client authentication (e.g. to support binding access tokens to a TLS client authentication (e.g. to support binding access tokens to a TLS
client certificate for public clients) is also possible. The client certificate for public clients) is also possible. The
authorization server would configure the TLS stack in the same manor authorization server would configure the TLS stack in the same manner
as for the Public Key method such that it does not verify that the as for the Self-Signed Certificate method such that it does not
certificate presented by the client during the handshake is signed by verify that the certificate presented by the client during the
a trusted CA. Individual instances of a public client would then handshake is signed by a trusted CA. Individual instances of a
create a self-signed certificate for mutual TLS with the public client would then create a self-signed certificate for mutual
authorization server and resource server. The authorization server TLS with the authorization server and resource server. The
would not authenticate the client at the OAuth layer but would bind authorization server would not authenticate the client at the OAuth
issued access tokens to the certificate, which the client has proven layer but would bind issued access tokens to the certificate, which
possession of the corresponding private key. The access token is the client has proven possession of the corresponding private key.
then mutual TLS sender constrained and can only be used by the client The access token is then mutual TLS sender constrained and can only
possessing the certificate and private key and utilizing them to be used by the client possessing the certificate and private key and
negotiate mutual TLS on connections to the resource server. 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.
5. IANA Considerations 5. IANA Considerations
5.1. JWT Confirmation Methods Registration 5.1. 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].
5.1.1. Registry Contents
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 ]]
5.2. OAuth Authorization Server Metadata Registration 5.2. 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].
5.2.1. Registry Contents
o Metadata Name: "mutual_tls_sender_constrained_access_tokens" o Metadata Name: "mutual_tls_sender_constrained_access_tokens"
o Metadata Description: Indicates server support for mutual TLS o Metadata Description: Indicates authorization server support for
sender constraint access tokens. mutual TLS sender constrained access tokens.
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 2.2 of [[ this specification ]] o Specification Document(s): Section 3.3 of [[ this specification ]]
5.3. Token Endpoint Authentication Method Registration 5.3. 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].
5.3.1. Registry Contents
o Token Endpoint Authentication Method Name: "tls_client_auth" o Token Endpoint Authentication Method Name: "tls_client_auth"
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 2.2 of [[ this specification ]] o Specification Document(s): Section 2.1.1 of [[ this specification
]]
o Token Endpoint Authentication Method Name: o Token Endpoint Authentication Method Name:
"pub_key_tls_client_auth" "self_signed_tls_client_auth"
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 2.2 of [[ this specification ]] o Specification Document(s): Section 2.2.1 of [[ this specification
]]
5.4. OAuth Token Introspection Response Registration 5.4. OAuth Token Introspection Response Registration
This specification requests registration of the following value in This specification requests registration of the following value in
the IANA "OAuth Token Introspection Response" registry the IANA "OAuth Token Introspection Response" registry
[IANA.OAuth.Parameters] established by [RFC7662]. [IANA.OAuth.Parameters] established by [RFC7662].
5.4.1. Registry Contents
o Claim Name: "cnf" o Claim Name: "cnf"
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 ]]
5.5. OAuth Dynamic Client Registration Metadata Registration 5.5. 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]:
5.5.1. Registry Contents
o Client Metadata Name: o Client Metadata Name:
"mutual_tls_sender_constrained_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 constraint access tokens. use mutual TLS sender constrained access tokens.
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 2.3 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 2.3 of [[ this specification ]] o Specification Document(s): Section 2.1.2 of [[ this specification
]]
o Client Metadata Name: "tls_client_auth_root_dn"
o Client Metadata Description: String value specifying the expected
distinguished name of the root issuer of the client certificate
o Change Controller: IESG
o Specification Document(s): Section 2.3 of [[ this specification ]]
6. Security Considerations 6. Security Considerations
6.1. TLS Versions and Best Practices 6.1. 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 latest version that is widely deployed. However, this writing, it is latest version that is widely deployed. However, this
document is applicable with other TLS versions supporting 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
found in Recommendations for Secure Use of Transport Layer Security found in Recommendations for Secure Use of Transport Layer Security
(TLS) and Datagram Transport Layer Security (DTLS) [BCP195]. (TLS) and Datagram Transport Layer Security (DTLS) [BCP195].
6.2. X.509 Certificate Spoofing 6.2. X.509 Certificate Spoofing
If the PKI method is used, an attacker could try to impersonate a If the PKI method is used, an attacker could try to impersonate a
client using a certificate for the same DN issued by another CA, client using a certificate for the same DN issued by another CA,
which the authorization server trusts. which the authorization server trusts. To cope with that threat, the
authorization server may decide to only accept a limited number of
There are two ways to cope with that threat: the authorization server CAs whose certificate issuance policy meets its security
may decide to only accept a limited number of CAs whose certificate requirements.
issuance policy meets its security requirements. Alternatively or in
addition, the client may want to explicitly prescribe the CA it will
use for obtaining its certificates. The latter is supported by this
document with the client registration parameter
"tls_client_auth_root_dn".
7. References 7. References
7.1. Normative References 7.1. Normative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre, [BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/bcp195>. 2015, <http://www.rfc-editor.org/info/bcp195>.
[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,
<http://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,
<http://www.rfc-editor.org/info/rfc4514>. <https://www.rfc-editor.org/info/rfc4514>.
[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,
<http://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,
<http://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012, RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>. <https://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750, Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012, DOI 10.17487/RFC6750, October 2012,
<http://www.rfc-editor.org/info/rfc6750>. <https://www.rfc-editor.org/info/rfc6750>.
[RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of- [RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key Semantics for JSON Web Tokens (JWTs)", Possession Key Semantics for JSON Web Tokens (JWTs)",
RFC 7800, DOI 10.17487/RFC7800, April 2016, RFC 7800, DOI 10.17487/RFC7800, April 2016,
<http://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
[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-04 (work in progress), August 2016. discovery-07 (work in progress), September 2017.
[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] [OpenID.Discovery]
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
Connect Discovery 1.0", February 2014. Connect Discovery 1.0", August 2015,
<http://openid.net/specs/
openid-connect-discovery-1_0.html>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/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,
<http://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
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>. <https://www.rfc-editor.org/info/rfc7519>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and [RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol", P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015, RFC 7591, DOI 10.17487/RFC7591, July 2015,
<http://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,
<http://www.rfc-editor.org/info/rfc7662>. <https://www.rfc-editor.org/info/rfc7662>.
Appendix A. Acknowledgements Appendix A. 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 that informed some of the content of
this document. 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, Phil Hunt, Sean Beryozkin, Vladimir Dzhuvinov, Samuel Erdtman, Phil Hunt, Sean
Leonard, Kepeng Li, James Manger, Jim Manico, Nov Matake, Sascha Leonard, Kepeng Li, James Manger, Jim Manico, Nov Matake, Sascha
Preibisch, Justin Richer, Dave Tonge, and Hannes Tschofenig. Preibisch, Justin Richer, Dave Tonge, and Hannes Tschofenig.
Appendix B. Document(s) History Appendix B. 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-04
o Change the name of the 'Public Key method' to the more accurate
'Self-Signed Certificate method' and also change the associated
authentication method metadata value to
"self_signed_tls_client_auth".
o Removed the "tls_client_auth_root_dn" client metadata field as
discussed in https://mailarchive.ietf.org/arch/msg/oauth/
swDV2y0be6o8czGKQi1eJV-g8qc
o Update draft-ietf-oauth-discovery reference to -07
o Clarify that MTLS client authentication isn't exclusive to the
token endpoint and can be used with other endpoints, e.g. RFC
7009 revocation and 7662 introspection, that utilize client
authentication as discussed in
https://mailarchive.ietf.org/arch/msg/oauth/
bZ6mft0G7D3ccebhOxnEYUv4puI
o Reorganize the document somewhat in an attempt to more clearly
make a distinction between mTLS client authentication and
certificate bound access tokens as well as a more clear
delineation between the two (PKI/Public key) methods for client
authentication
o Editorial fixes and clarifications
draft-ietf-oauth-mtls-03 draft-ietf-oauth-mtls-03
o Introduced metadata and client registration parameter to publish o Introduced metadata and client registration parameter to publish
and request support for mutual TLS sender constrained access and request support for mutual TLS sender constrained access
tokens tokens
o Added description of two methods of binding the cert and client, o Added description of two methods of binding the cert and client,
PKI and Public Key. PKI and Public Key.
o Indicated that the "tls_client_auth" authentication method is for o Indicated that the "tls_client_auth" authentication method is for
the PKI method and introduced "pub_key_tls_client_auth" for the the PKI method and introduced "pub_key_tls_client_auth" for the
Public Key method Public Key method
 End of changes. 68 change blocks. 
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