OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens
RFC 8705

Document Type RFC - Proposed Standard (February 2020; No errata)
Authors Brian Campbell  , John Bradley  , Nat Sakimura  , Torsten Lodderstedt 
Last updated 2020-03-09
Replaces draft-campbell-oauth-mtls
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IESG IESG state RFC 8705 (Proposed Standard)
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Send notices to Rifaat Shekh-Yusef <rifaat.ietf@gmail.com>
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Internet Engineering Task Force (IETF)                       B. Campbell
Request for Comments: 8705                                 Ping Identity
Category: Standards Track                                     J. Bradley
ISSN: 2070-1721                                                   Yubico
                                                             N. Sakimura
                                               Nomura Research Institute
                                                          T. Lodderstedt
                                                              YES.com AG
                                                           February 2020

    OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound
                             Access Tokens


   This document describes OAuth client authentication and certificate-
   bound access and refresh tokens using mutual Transport Layer Security
   (TLS) authentication with X.509 certificates.  OAuth clients are
   provided a mechanism for authentication to the authorization server
   using mutual TLS, based on either self-signed certificates or public
   key infrastructure (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

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction
     1.1.  Requirements Notation and Conventions
     1.2.  Terminology
   2.  Mutual TLS for OAuth Client Authentication
     2.1.  PKI Mutual-TLS Method
       2.1.1.  PKI Method Metadata Value
       2.1.2.  Client Registration Metadata
     2.2.  Self-Signed Certificate Mutual-TLS Method
       2.2.1.  Self-Signed Method Metadata Value
       2.2.2.  Client Registration Metadata
   3.  Mutual-TLS Client Certificate-Bound Access Tokens
     3.1.  JWT Certificate Thumbprint Confirmation Method
     3.2.  Confirmation Method for Token Introspection
     3.3.  Authorization Server Metadata
     3.4.  Client Registration Metadata
   4.  Public Clients and Certificate-Bound Tokens
   5.  Metadata for Mutual-TLS Endpoint Aliases
   6.  Implementation Considerations
     6.1.  Authorization Server
     6.2.  Resource Server
     6.3.  Certificate Expiration and Bound Access Tokens
     6.4.  Implicit Grant Unsupported
     6.5.  TLS Termination
   7.  Security Considerations
     7.1.  Certificate-Bound Refresh Tokens
     7.2.  Certificate Thumbprint Binding
     7.3.  TLS Versions and Best Practices
     7.4.  X.509 Certificate Spoofing
     7.5.  X.509 Certificate Parsing and Validation Complexity
   8.  Privacy Considerations
   9.  IANA Considerations
     9.1.  JWT Confirmation Methods Registration
     9.2.  Authorization Server Metadata Registration
     9.3.  Token Endpoint Authentication Method Registration
     9.4.  Token Introspection Response Registration
     9.5.  Dynamic Client Registration Metadata Registration
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Appendix A.  Example "cnf" Claim, Certificate, and JWK
   Appendix B.  Relationship to Token Binding
   Authors' Addresses

1.  Introduction

   The OAuth 2.0 Authorization Framework [RFC6749] enables third-party
   client applications to obtain delegated access to protected
   resources.  In the prototypical abstract OAuth flow, illustrated in
   Figure 1, the client obtains an access token from an entity known as
   an authorization server and then uses that token when accessing
   protected resources, such as HTTPS APIs.

     +--------+                                 +---------------+
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