Proof Key for Code Exchange by OAuth Public Clients
RFC 7636

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Internet Engineering Task Force (IETF)                  N. Sakimura, Ed.
Request for Comments: 7636                     Nomura Research Institute
Category: Standards Track                                     J. Bradley
ISSN: 2070-1721                                            Ping Identity
                                                              N. Agarwal
                                                                  Google
                                                          September 2015

          Proof Key for Code Exchange by OAuth Public Clients

Abstract

   OAuth 2.0 public clients utilizing the Authorization Code Grant are
   susceptible to the authorization code interception attack.  This
   specification describes the attack as well as a technique to mitigate
   against the threat through the use of Proof Key for Code Exchange
   (PKCE, pronounced "pixy").

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7636.

Copyright Notice

   Copyright (c) 2015 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
   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.

Sakimura, et al.             Standards Track                    [Page 1]
RFC 7636                       OAUTH PKCE                 September 2015

Table of Contents

   1. Introduction ....................................................3
      1.1. Protocol Flow ..............................................5
   2. Notational Conventions ..........................................6
   3. Terminology .....................................................7
      3.1. Abbreviations ..............................................7
   4. Protocol ........................................................8
      4.1. Client Creates a Code Verifier .............................8
      4.2. Client Creates the Code Challenge ..........................8
      4.3. Client Sends the Code Challenge with the
           Authorization Request ......................................9
      4.4. Server Returns the Code ....................................9
           4.4.1. Error Response ......................................9
      4.5. Client Sends the Authorization Code and the Code
           Verifier to the Token Endpoint ............................10
      4.6. Server Verifies code_verifier before Returning the
           Tokens ....................................................10
   5. Compatibility ..................................................11
   6. IANA Considerations ............................................11
      6.1. OAuth Parameters Registry .................................11
      6.2. PKCE Code Challenge Method Registry .......................11
           6.2.1. Registration Template ..............................12
           6.2.2. Initial Registry Contents ..........................13
   7. Security Considerations ........................................13
      7.1. Entropy of the code_verifier ..............................13
      7.2. Protection against Eavesdroppers ..........................13
      7.3. Salting the code_challenge ................................14
      7.4. OAuth Security Considerations .............................14
      7.5. TLS Security Considerations ...............................15
   8. References .....................................................15
      8.1. Normative References ......................................15
      8.2. Informative References ....................................16
   Appendix A.  Notes on Implementing Base64url Encoding without
                Padding  .............................................17
   Appendix B.  Example for the S256 code_challenge_method ...........17
   Acknowledgements ..................................................19
   Authors' Addresses ................................................20

Sakimura, et al.             Standards Track                    [Page 2]