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Versions: 00 draft-ietf-oauth-token-binding

OAuth Working Group                                          B. Campbell
Internet-Draft                                                J. Bradley
Intended status: Standards Track                           Ping Identity
Expires: January 9, 2017                                        M. Jones
                                                               Microsoft
                                                            July 8, 2016


    A Token Binding method for OAuth 2.0 Proof Key for Code Exchange
                     draft-campbell-oauth-tbpkce-00

Abstract

   This specification describes a Proof Key for Code Exchange (PKCE)
   [RFC7636] method utilizing Token Binding over HTTP
   [I-D.ietf-tokbind-https] to cryptographically bind the OAuth 2.0
   [RFC6749] authorization code to a key pair on the client, which it
   proves possession of during the access token request with the
   authorization code.

Status of This Memo

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

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

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

   This Internet-Draft will expire on January 9, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (http://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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation and Conventions . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Code Challenge  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Code Verifier . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  PKCE Code Challenge Method Registration . . . . . . . . .   4
       5.1.1.  Registry Contents . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Appendix B.  Document History . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   This specification minimally describes an OAuth 2.0 [RFC6749] PKCE
   [RFC7636] method based on the Token Binding Protocol
   [I-D.ietf-tokbind-protocol] and Token Binding over HTTP
   [I-D.ietf-tokbind-https].  The general details and motivations of
   PKCE are discussed in that document and this specification defines
   only the additional pieces needed for a Token Binding PKCE method.

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].

1.2.  Terminology

   This specification uses the terms "authorization code",
   "authorization endpoint", "authorization server", "authorization
   request", "access token request", "client", and "token endpoint"
   defined by OAuth 2.0 [RFC6749], and the terms "Provided", "Token
   Binding" and "Token Binding ID" defined by Token Binding over HTTP
   [I-D.ietf-tokbind-https].







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2.  Code Challenge

   As defined in Proof Key for Code Exchange [RFC7636], the client sends
   the code challenge as part of the OAuth 2.0 Authorization Request
   with the two additional parameters: "code_challenge" and
   "code_challenge_method".

   For the Token Binding method of PKCE defined herein, "tb2" is used
   for the value of the "code_challenge_method" parameter.

   The value of the "code_challenge" parameter is the base64url encoding
   (per Section 5 of [RFC4648] with all trailing pad ('=') characters
   omitted and without the inclusion of any line breaks or whitespace)
   of the SHA-256 hash [RFC6234] of the Provided Token Binding ID that
   the client will use when calling the authorization server's token
   endpoint.  Note that, prior to making the authorization request, the
   client may need to establish a TLS connection between itself and the
   authorization server's token endpoint in order to obtain the
   appropriate Token Binding ID.

   When the authorization server issues the authorization code in the
   authorization response, it associates the code challenge and method
   values with the authorization code so it can be verified later when
   the code is presented in the access token request.

3.  Code Verifier

   Upon receipt of the authorization code, the client sends the access
   token request to the token endpoint.  The Token Binding Protocol
   [I-D.ietf-tokbind-protocol] is negotiated on the TLS connection
   between the client and the authorization server and the "Sec-Token-
   Binding" header, as defined in Token Binding over HTTP
   [I-D.ietf-tokbind-https], is included in the access token request.
   The authorization server extracts the Provided Token Binding ID from
   the header value, hashes it with SHA-256, and compares it to the
   "code_challenge" value previously associated with the authorization
   code.  If the values match, the token endpoint MUST continue
   processing as normal (as defined by OAuth 2.0 [RFC6749]).  If the
   values do not match, an error response indicating "invalid_grant"
   MUST be returned.

   The "Sec-Token-Binding" header contains sufficient information for
   verification of the authorization code and its association to the
   original authorization request.  However, PKCE [RFC7636] requires
   that a "code_verifier" parameter be sent with the access token
   request, so the static value "provided" is used to meet that
   requirement and indicate that the Provided Token Binding ID is used
   for the verification.



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4.  Security Considerations

   TBD

5.  IANA Considerations

5.1.  PKCE Code Challenge Method Registration

   This specification requests registration of the following Code
   Challenge Method Parameter Name in the IANA "PKCE Code Challenge
   Methods" registry [IANA.OAuth.Parameters] established by [RFC7636].

5.1.1.  Registry Contents

   o  Code Challenge Method Parameter Name: tb2
   o  Change controller: IESG
   o  Specification document(s): Section 2 of [[ this specification ]]

6.  Normative References

   [I-D.ietf-tokbind-https]
              Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
              Hodges, "Token Binding over HTTP", draft-ietf-tokbind-
              https-03 (work in progress), March 2016.

   [I-D.ietf-tokbind-protocol]
              Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
              Hodges, "The Token Binding Protocol Version 1.0", draft-
              ietf-tokbind-protocol-06 (work in progress), May 2016.

   [IANA.OAuth.Parameters]
              IANA, "OAuth Parameters",
              <http://www.iana.org/assignments/oauth-parameters>.

   [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>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI
              10.17487/RFC6234, May 2011,
              <http://www.rfc-editor.org/info/rfc6234>.




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   [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>.

   [RFC7636]  Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
              for Code Exchange by OAuth Public Clients", RFC 7636, DOI
              10.17487/RFC7636, September 2015,
              <http://www.rfc-editor.org/info/rfc7636>.

Appendix A.  Acknowledgements

   Dirk Balfanz, William Dennis (and others?) also provided input to
   this specification.

Appendix B.  Document History

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

   draft-campbell-oauth-tbpkce-00

   o  Initial version.

Authors' Addresses

   Brian Campbell
   Ping Identity

   Email: brian.d.campbell@gmail.com
   URI:   https://twitter.com/__b_c


   John Bradley
   Ping Identity

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


   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/








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