Mutual X.509 Transport Layer Security (TLS) Authentication for OAuth Clients
draft-campbell-oauth-tls-client-auth-00

OAuth Working Group                                          B. Campbell
Internet-Draft                                                J. Bradley
Intended status: Standards Track                           Ping Identity
Expires: April 13, 2017                                 October 10, 2016


  Mutual X.509 Transport Layer Security (TLS) Authentication for OAuth
                                Clients
                draft-campbell-oauth-tls-client-auth-00

Abstract

   This document describes X.509 certificates as OAuth client
   credentials using Transport Layer Security (TLS) mutual
   authentication as a mechanism for client authentication to the
   authorization server's token endpoint.

Status of This Memo

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   This Internet-Draft will expire on April 13, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation and Conventions . . . . . . . . . .   2
   2.  Mutual TLS for Client Authentication  . . . . . . . . . . . .   2
   3.  Metadata  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Token Endpoint Authentication Method Registration . . . .   3
       4.1.1.  Registry Contents . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
     5.1.  TLS Versions and Best Practices . . . . . . . . . . . . .   3
     5.2.  Client Identity Binding . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Appendix B.  Document History . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The OAuth 2.0 Authorization Framework [RFC6749] defines a shared
   secret method of client authentication but also allows for the
   definition and use of additional client authentication mechanisms
   when interacting with the authorization server's token endpoint.
   This document describes an additional mechanism of client
   authentication utilizing mutual TLS [RFC5246] certificate-based
   authentication.

1.1.  Requirements Notation and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

2.  Mutual TLS for Client Authentication

   The following section defines, as an extension of OAuth 2.0,
   Section 2.3 [RFC6749], the use of mutual TLS as client credentials.
   OAuth 2.0 requires that access token requests by the client to the
   token endpoint use TLS.  In order to utilize TLS for client
   authentication, the TLS connection MUST have been established or
   reestablished with mutual X.509 certificate authentication (i.e. the
   Client Certificate and Certificate Verify messages are sent during
   the TLS Handshake [RFC5246]).





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   For all access token requests to the token endpoint, regardless of
   the grant type used, the client MUST include the "client_id"
   parameter, described in OAuth 2.0, Section 2.2 [RFC6749].  The
   presence of the "client_id" parameter enables the authorization
   server to easily identify the client independently from the content
   of the certificate and allows for trust models to vary as appropriate
   for a given deployment.  The authorization server can locate the
   client configuration by the client identifier and check the
   certificate presented in the TLS Handshake against the expected
   credentials for that client.

3.  Metadata

   The value "tls_client_auth" is used to indicate mutual TLS as an
   authentication method to the token endpoint for the
   "token_endpoint_auth_methods_supported" client metadata field defined
   in [RFC7591], Section 2.

   The same "tls_client_auth" value can also indicate server support for
   mutual TLS as a client authentication method in authorization server
   metadata such as [OpenID.Discovery] and [I-D.ietf-oauth-discovery].

4.  IANA Considerations

4.1.  Token Endpoint Authentication Method Registration

   This specification requests registration of the following value in
   the IANA "OAuth Token Endpoint Authentication Methods" registry
   [IANA.OAuthTEAuthnMeths] established by [RFC7591].

4.1.1.  Registry Contents

   o  Token Endpoint Authentication Method Name: "tls_client_auth"
   o  Change Controller: IESG
   o  Specification Document(s): [[ this specification ]]

5.  Security Considerations

5.1.  TLS Versions and Best Practices

   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
   document is applicable with other TLS versions supporting
   certificate-based client authentication.  Implementation security
   considerations for TLS, including version recommendations, can be
   found in Recommendations for Secure Use of Transport Layer Security
   (TLS) and Datagram Transport Layer Security (DTLS) [BCP195].




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5.2.  Client Identity Binding

   No specifc method of binding a certificate to a client identifier is
   prescribed by this document.  However, some method should employed so
   that, in addition to proving possession of the private key
   corresponding to the certificate, the client identity is also bound
   to the certificate.  One such binding would be to configure for the
   client a value that the certificate must contain in the subject field
   or the subjectAltName extension and possibly a restricted set of
   trust anchors.  An alternative method would be to configure a public
   key for the client directly that would have to match the subject
   public key info of the certificate.

6.  References

6.1.  Normative References

   [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/bcp195>.

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

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

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

6.2.  Informative References

   [I-D.ietf-oauth-discovery]
              Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
              Authorization Server Metadata", draft-ietf-oauth-
              discovery-04 (work in progress), August 2016.

   [IANA.OAuthTEAuthnMeths]
              IANA, "OAuth Token Endpoint Authentication Methods",
              <http://www.iana.org/assignments/oauth-parameters/
              oauth-parameters.xhtml#token-endpoint-auth-method>.



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   [OpenID.Discovery]
              Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
              Connect Discovery 1.0", February 2014.

   [RFC7591]  Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
              P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
              RFC 7591, DOI 10.17487/RFC7591, July 2015,
              <http://www.rfc-editor.org/info/rfc7591>.

Appendix A.  Acknowledgements

   Scott "not Tomlinson" Tomilson and Matt Peterson were involved in the
   original design and implementation work that informed the content of
   this document.

Appendix B.  Document History

   [[ to be removed by the RFC Editor before publication as an RFC ]]

   -00

   o  Initial draft.

Authors' Addresses

   Brian Campbell
   Ping Identity

   Email: brian.d.campbell@gmail.com


   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com
   URI:   http://www.thread-safe.com/















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