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Network Working Group                                    J. Bradley, Ed.
Internet-Draft                                                      Ping
Intended status: Experimental Protocol                    T. Lodderstedt
Expires: April 28, 2015                              Deutsche Telekom AG
                                                             H. Zandbelt
                                                                    Ping
                                                        October 27, 2014

       Encoding claims in the OAuth 2 state parameter using a JWT
                draft-bradley-oauth-jwt-encoded-state-02

Abstract

   This draft provides a method for a client to encode one or more
   elements encoding information about the session into the OAuth 2
   "state" parameter.

Requirements Language

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

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 April 28, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.









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   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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  The state JSON Web Token claims  . . . . . . . . . . . . . . .  2
   3.  Validating the state parameter . . . . . . . . . . . . . . . .  5
   4.  Creating a Request Forgery Protection (rfp) claim value. . . .  5
     4.1.  Stateful Clients.  . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Stateless Clients. . . . . . . . . . . . . . . . . . . . .  5
     4.3.  Responses Initiated by the Issuer  . . . . . . . . . . . .  6
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  6
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  7

1.  Introduction

   In the OAuth 2.0 Authorization protocol [RFC6749] , the Authorization
   server SHOULD perform an exact string comparison of the
   "redirect_uri" parameter with the "redirect_uri" parameter registered
   by by the client.  This is essential for preventing token leakage to
   third parties in the OAuth implicit flow.

   As a result of this clients can not safely add extra query parameters
   to the "redirect_uri" parameter that encode additional client state
   information.

   The Client MUST use the "state" parameter to encode both Cross Site
   Request Forgery protection and any other state information it wishes
   to preserve for itself regarding the authorization request.

   This draft proposes a mechanism whereby multiple state attributes can
   be encoded into a JSON Web Token [JWT] for use as the value of the
   "state" parameter.

   The JWT may be sent without integrity protection, with integrity
   protection [JWA], or with both integrity and confidentiality
   protection [JWE].  The client is free to choose the appropriate
   protection for its use-case as the "state" parameter is treated as
   opaque by the Authorization Server (AS).

2.  The state JSON Web Token claims



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   The OAuth Authorization request "state" parameter consists of a
   [JWT], optionally signed with [JWS] or encrypted with [JWE], whose
   payload contains claims as defined here.

   rfp
      REQUIRED. string containing a verifiable identifier for the
      browser session, that cannot be guessed by a third party.  The
      verification of this element by the client protects it from
      accepting authorization responses generated in response to forged
      requests generated by third parties.

   kid
      RECOMMENDED if signed or encrypted.  Identifier of the key used to
      sign this state token at the issuer.  Identifier of the key used
      to encrypt this JWT state token at the issuer.  This SHOULD be
      included in the [JWE] header.

   iat
      OPTIONAL. Timestamp of when this Authorization Request was issued.

   exp
      OPTIONAL. The "exp" (expiration time) claim identifies the
      expiration time on or after which the JWT MUST NOT be accepted for
      processing.  The processing of the "exp" claim requires that the
      current date/time MUST be before the expiration date/time listed
      in the "exp" claim.  Implementers MAY provide for some small
      leeway, usually no more than a few minutes, to account for clock
      skew.  Its value MUST be a number containing an IntDate value.
      Use of this claim is OPTIONAL.  This is RECOMMENDED if the [JWT]
      state token is being produced by the AS.

   iss
      OPTIONAL. string identifying the party that issued this state
      value.

   aud
      OPTIONAL. string identifying the client that this state value is
      intended for.

   target_link_uri
      OPTIONAL. URI containing the location the user agent is to be
      redirected to after authorization.

   as
      OPTIONAL. string identifying the authorization server that this
      request was sent to.

   jti






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      RECOMMENDED. The "jti" (JWT ID) claim provides a unique identifier
      for the JWT.  The identifier value MUST be assigned in a manner
      that ensures that there is a negligible probability that the same
      value will be accidentally assigned to a different data object.
      The "jti" claim can be used to prevent the JWT from being
      replayed.  The "jti" value is a case-sensitive string.  Use of
      this claim is OPTIONAL.

   at_hash
      OPTIONAL.  Access Token hash value.  Its value is the base64url
      encoding of the left-most half of the hash of the octets of the
      ASCII representation of the "access_token" value, where the hash
      algorithm used is the hash algorithm used in the "alg" parameter
      of the State Token's JWS [JWS] header.  For instance, if the "alg"
      is "RS256", hash the "access_token" value with SHA-256, then take
      the left-most 128 bits and base64url encode them.  The "at_hash"
      value is a case sensitive string.  This is REQUIRED if the [JWT]
      state token is being produced by the AS and issued with a
      "access_token" in the authorization response.

   c_hash
      OPTIONAL.  Code hash value.  Its value is the base64url encoding
      of the left-most half of the hash of the octets of the ASCII
      representation of the "code" value, where the hash algorithm used
      is the hash algorithm used in the "alg" header parameter of the
      State Token's JWS [JWS] header.  For instance, if the "alg" is
      "HS512", hash the "code" value with SHA-512, then take the left-
      most 256 bits and base64url encode them.  The "c_hash" value is a
      case sensitive string.  This is REQUIRED if the [JWT] state token
      is being produced by the AS and issued with a "code" in the
      authorization response.

   The issuer may add additional claims to the token.  The producer and
   the consumer of the JWT are the same or closely related entities so
   collision resistance of claim names should not be a concern.

   The issuer SHOULD sign the JWT with [JWS] in such a way that it can
   verify the signature.  The [JWA] algorithm HS256 with a key of
   256bits is recommended.

   The issuer MAY sign the [JWT] with [JWA] algorithm none if integrity
   protecting the contents of the "state" parameter is not required.

   If the "state" parameter contains information the client doesn't want
   to disclose to the Authorization server or user, the issuer MAY
   encrypt the [JWT] with [JWE].  The JWA [JWA] algorithm ("alg") of
   "dir" and encryption algorithm ("enc") of "A128CBC-HS256" are
   recommended for symmetric encryption.

   In the case of the "state" value being created by the Issuer the





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   "iss" and "aud" claims MUST be included in the JWT. The jwt MUST also
   be signed with [JWS].  If the State token is issued with a code
   "c_hash" MUST be included.  If the State Token is issued with a
   Access Token "at_hash" MUST be included.

3.  Validating the state parameter

   Upon receiving a state parameter the client must validate its
   integrity.  The client parses it as a JWT. It then verifies the
   signature of the JWT (if signed) using [JWS].  The key used to sign
   the [JWT] MAY be indicated by the kid field.  The client MAY use
   other means to validate the JWT and determine its authenticity.

   The client then reads the fields inside the [JWT] and uses these to
   configure the user experience and security parameters of the
   authorization.

   The "rfp" claim MUST be validated by the client by comparing it to
   the secret information that it used to create the "rfp" value.

4.  Creating a Request Forgery Protection (rfp) claim value.

   The client MUST create a value that cannot be guessed by a third
   party attacker and used to forge requests.  There are many possible
   ways to create this value.  For reference two common ways will be
   listed.

   It is completely up to the purview of the particular client which
   generation methods, and which claims, they will accept.

4.1.  Stateful Clients.

   Many clients that are web servers maintain session state for browsers
   in a server side store.

   These clients can generate a random value with sufficient entropy
   that an attacker cannot guess future values.  This value can be
   stored in the server side store and used directly as the value of
   "rfp".

4.2.  Stateless Clients.

   Some clients that are web servers maintain session state for browsers
   using browser stored cookies or HTML5 local storage.

   These clients can generate a hash value based on a HTTPS: bound
   session cookie or other browser side information that is not
   accessible to third parties.  This hash value can directly as the
   value of "xsrf".

   While OAuth strongly recommends that clients use TLS to secure their
   endpoints, if a client is not using TLS it MUST produce the value of
   "rfp" by using a HMAC algorithm with a secret known only to itself
   over the browser stored information.

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4.3.  Responses Initiated by the Issuer

   Some clients may be willing to rely on the Authorization server
   providing protection for Cross Site Request Forgery.  In Cases where
   the Authorization server and the client have a pre-established
   relationship, and the client is willing to accept flows initiated by
   the Authorization server, the string "iss" may be used as the value
   of "rfp".

5.  IANA Considerations

   [ maybe we register the "rfp" claim above?  ]

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

6.  Security Considerations

   Some information in the state JWT such as target_link_uri value for
   redirecting the user to the application might have some security
   impact is the user modifies them intentionally or unintentionally.
   To prevent tampering with the "state" value the client may integrity
   protect the contents of the JWT.

   The client may have information that it wants to protect from
   disclosure to the Authorization server, in logs, to proxies, or to
   the user.  In this case encrypting the JWT as a JWE is required to
   protect the confidentiality of the state information.

7.  Acknowledgements

8.  References

   [JWA]      Jones, M.B., "JSON Web Algorithms (JWA)", Internet-Draft
              draft-ietf-jose-json-web-algorithms, Oct 2014.

   [JWE]      Jones, M.B. and J. Hildebrand, "JSON Web Encryption
              (JWE)", Internet-Draft draft-ietf-jose-json-web-
              encryption, Oct 2014.

   [JWS]      Jones, M.B., Bradley, J. and N. Sakimura, "JSON Web
              Signature (JWS)", Internet-Draft draft-ietf-jose-json-web-
              signature, Oct 2014.

   [JWT]      Jones, M.B., Bradley, J. and N. Sakimura, "JSON Web Token
              (JWT)", Internet-Draft draft-ietf-oauth-json-web-token,
              Oct 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


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   [RFC6749]  Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
              6749, October 2012.

Authors' Addresses

   John Bradley, editor
   Ping Identity

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


   Dr.-Ing. Torsten Lodderstedt
   Deutsche Telekom AG

   Email: torsten@lodderstedt.net


   Hans Zandbelt
   Ping Identity

   Email: hzandbelt@pingidentity.com
   URI:   http://hanszandbelt.wordpress.com






























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