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Network Working Group                                           M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                                D. Hardt
Expires: March 25, 2012                                      independent
                                                             D. Recordon
                                                                Facebook
                                                      September 22, 2011


          The OAuth 2.0 Authorization Protocol: Bearer Tokens
                     draft-ietf-oauth-v2-bearer-09

Abstract

   This specification describes how to use bearer tokens in HTTP
   requests to access OAuth 2.0 protected resources.

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 March 25, 2012.

Copyright Notice

   Copyright (c) 2011 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.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Authenticated Requests . . . . . . . . . . . . . . . . . . . .  5
     2.1.  The Authorization Request Header Field . . . . . . . . . .  5
     2.2.  Form-Encoded Body Parameter  . . . . . . . . . . . . . . .  5
     2.3.  URI Query Parameter  . . . . . . . . . . . . . . . . . . .  6
     2.4.  The WWW-Authenticate Response Header Field . . . . . . . .  7
       2.4.1.  Error Codes  . . . . . . . . . . . . . . . . . . . . .  8
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     3.1.  Security Threats . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Threat Mitigation  . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Summary of Recommendations . . . . . . . . . . . . . . . . 11
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  OAuth Access Token Type Registration . . . . . . . . . . . 12
       4.1.1.  The "Bearer" OAuth Access Token Type . . . . . . . . . 12
     4.2.  Authentication Scheme Registration . . . . . . . . . . . . 12
       4.2.1.  The "Bearer" Authentication Scheme . . . . . . . . . . 12
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 14
   Appendix B.  Document History  . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
























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1.  Introduction

   OAuth enables clients to access protected resources by obtaining an
   access token, which is defined in [I-D.ietf-oauth-v2] as "a string
   representing an access authorization issued to the client", rather
   than using the resource owner's credentials directly.

   Tokens are issued to clients by an authorization server with the
   approval of the resource owner.  The client uses the access token to
   access the protected resources hosted by the resource server.  This
   specification describes how to make protected resource requests when
   the OAuth access token is a bearer token.

   This specification defines the use of bearer tokens with OAuth over
   HTTP [RFC2616] using TLS [RFC5246].  Other specifications may extend
   it for use with other transport protocols.

1.1.  Notational Conventions

   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 [RFC2119].

   This document uses the Augmented Backus-Naur Form (ABNF) notation of
   [I-D.ietf-httpbis-p1-messaging], which is based upon the Augmented
   Backus-Naur Form (ABNF) notation of [RFC5234].  Additionally, the
   following rules are included from [I-D.ietf-httpbis-p7-auth]:
   b64token, auth-param, and realm; from
   [I-D.ietf-httpbis-p1-messaging]: quoted-string; and from [RFC3986]:
   URI-Reference.

   Unless otherwise noted, all the protocol parameter names and values
   are case sensitive.

1.2.  Terminology

   Bearer Token
      A security token with the property that any party in possession of
      the token (a "bearer") can use the token in any way that any other
      party in possession of it can.  Using a bearer token does not
      require a bearer to prove possession of cryptographic key material
      (proof-of-possession).

   All other terms are as defined in [I-D.ietf-oauth-v2].







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1.3.  Overview

   OAuth provides a method for clients to access a protected resource on
   behalf of a resource owner.  In the general case, before a client can
   access a protected resource, it must first obtain authorization
   (access grant) from the resource owner and then exchange the access
   grant for an access token (representing the grant's scope, duration,
   and other attributes).  The client accesses the protected resource by
   presenting the access token to the resource server.  In some cases, a
   client can directly present its own credentials to an authorization
   server to obtain an access token without having to first obtain an
   access grant from a resource owner.

   The access token provides an abstraction layer, replacing different
   authorization constructs (e.g. username and password, assertion) for
   a single token understood by the resource server.  This abstraction
   enables issuing access tokens valid for a short time period, as well
   as removing the resource server's need to understand a wide range of
   authentication schemes.

   +--------+                               +---------------+
   |        |--(A)- Authorization Request ->|   Resource    |
   |        |                               |     Owner     |
   |        |<-(B)----- Access Grant -------|               |
   |        |                               +---------------+
   |        |
   |        |           Access Grant &      +---------------+
   |        |--(C)--- Client Credentials -->| Authorization |
   | Client |                               |     Server    |
   |        |<-(D)----- Access Token -------|               |
   |        |                               +---------------+
   |        |
   |        |                               +---------------+
   |        |--(E)----- Access Token ------>|    Resource   |
   |        |                               |     Server    |
   |        |<-(F)--- Protected Resource ---|               |
   +--------+                               +---------------+

                     Figure 1: Abstract Protocol Flow

   The abstract flow illustrated in Figure 1 describes the overall OAuth
   2.0 protocol architecture.  The following steps are specified within
   this document:

      E) The client makes a protected resource request to the resource
      server by presenting the access token.





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      F) The resource server validates the access token, and if valid,
      serves the request.


2.  Authenticated Requests

   Clients SHOULD make authenticated requests with a bearer token using
   the "Authorization" request header field defined by
   [I-D.ietf-httpbis-p7-auth].  Resource servers MUST accept
   authenticated requests using the "Bearer" HTTP authorization scheme
   as described in Section 2.1, and MAY support additional methods.

   Alternatively, clients MAY transmit the access token in the HTTP body
   when using the "application/x-www-form-urlencoded" content type as
   described in Section 2.2; or clients MAY transmit the access token in
   the HTTP request URI in the query component as described in
   Section 2.3.  Resource servers MAY support these alternative methods.

   Clients SHOULD NOT use the request body or URI unless the
   "Authorization" request header field is not available, and MUST NOT
   use more than one method to transmit the token in each request.
   Because of the Security Considerations (Section 3) associated with
   the URI method, it SHOULD NOT be used unless no other method is
   feasible.

2.1.  The Authorization Request Header Field

   The "Authorization" request header field is used by clients to make
   authenticated requests with bearer tokens.  The client uses the
   "Bearer" authentication scheme to transmit the access token in the
   request.

   For example:

   GET /resource HTTP/1.1
   Host: server.example.com
   Authorization: Bearer vF9dft4qmT

   The "Authorization" header field uses the framework defined by
   [I-D.ietf-httpbis-p7-auth] follows:

   credentials = "Bearer" 1*SP ( b64token / #auth-param )

2.2.  Form-Encoded Body Parameter

   When including the access token in the HTTP request entity-body, the
   client adds the access token to the request body using the
   "access_token" parameter.  The client MUST NOT use this method unless



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   the following conditions are met:

   o  The HTTP request entity-body is single-part.

   o  The entity-body follows the encoding requirements of the
      "application/x-www-form-urlencoded" content-type as defined by
      [W3C.REC-html401-19991224].

   o  The HTTP request entity-header includes the "Content-Type" header
      field set to "application/x-www-form-urlencoded".

   o  The HTTP request method is one for which the request body has
      defined semantics.  In particular, this means that the "GET"
      method MUST NOT be used.

   The entity-body can include other request-specific parameters, in
   which case, the "access_token" parameter MUST be properly separated
   from the request-specific parameters using "&" character(s) (ASCII
   code 38).

   For example, the client makes the following HTTP request using
   transport-layer security:

   POST /resource HTTP/1.1
   Host: server.example.com
   Content-Type: application/x-www-form-urlencoded

   access_token=vF9dft4qmT

   The "application/x-www-form-urlencoded" method SHOULD NOT be used
   except in application contexts where participating browsers do not
   have access to the "Authorization" request header field.

2.3.  URI Query Parameter

   When including the access token in the HTTP request URI, the client
   adds the access token to the request URI query component as defined
   by [RFC3986] using the "access_token" parameter.

   For example, the client makes the following HTTP request using
   transport-layer security:

   GET /resource?access_token=vF9dft4qmT HTTP/1.1
   Host: server.example.com

   The HTTP request URI query can include other request-specific
   parameters, in which case, the "access_token" parameter MUST be
   properly separated from the request-specific parameters using "&"



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   character(s) (ASCII code 38).

   For example:

   https://server.example.com/resource?x=y&access_token=vF9dft4qmT&p=q

   Because of the Security Considerations (Section 3) associated with
   the URI method, it SHOULD NOT be used unless no other method is
   feasible.

2.4.  The WWW-Authenticate Response Header Field

   If the protected resource request does not include authentication
   credentials or does not contain an access token that enables access
   to the protected resource, the resource server MUST include the HTTP
   "WWW-Authenticate" response header field; it MAY include it in
   response to other conditions as well.  The "WWW-Authenticate" header
   field uses the framework defined by [I-D.ietf-httpbis-p7-auth] as
   follows:

   challenge       = "Bearer" [ 1*SP 1#param ]

   param           = realm / scope /
                     error / error-desc / error-uri /
                     auth-param

   scope           = "scope" "=" <"> scope-v *( SP scope-v ) <">
   scope-v         = 1*quoted-char

   quoted-char     = ALPHA / DIGIT /
                     "!" / "#" / "$" / "%" / "&" / "'" / "(" / ")" /
                     "*" / "+" / "-" / "." / "/" / ":" / "<" / "=" /
                     ">" / "?" / "@" / "[" / "]" / "^" / "_" / "`" /
                     "{" / "|" / "}" / "~" / "\" / "," / ";"

   error           = "error" "=" quoted-string
   error-desc      = "error_description" "=" quoted-string
   error-uri       = "error_uri" "=" <"> URI-reference <">

   The "scope" attribute is a space-delimited list of scope values
   indicating the required scope of the access token for accessing the
   requested resource.  The "scope" attribute MUST NOT appear more than
   once.

   If the protected resource request included an access token and failed
   authentication, the resource server SHOULD include the "error"
   attribute to provide the client with the reason why the access
   request was declined.  The parameter value is described in



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   Section 2.4.1.  In addition, the resource server MAY include the
   "error_description" attribute to provide developers a UTF-8 encoded
   human-readable explanation, and the "error_uri" attribute with an
   absolute URI identifying a human-readable web page explaining the
   error.  The "error", "error_description", and "error_uri" attribute
   MUST NOT appear more than once.

   For example, in response to a protected resource request without
   authentication:

   HTTP/1.1 401 Unauthorized
   WWW-Authenticate: Bearer realm="example"

   And in response to a protected resource request with an
   authentication attempt using an expired access token:

   HTTP/1.1 401 Unauthorized
   WWW-Authenticate: Bearer realm="example",
                     error="invalid_token",
                     error_description="The access token expired"

2.4.1.  Error Codes

   When a request fails, the resource server responds using the
   appropriate HTTP status code (typically, 400, 401, or 403), and
   includes one of the following error codes in the response:

   invalid_request
         The request is missing a required parameter, includes an
         unsupported parameter or parameter value, repeats the same
         parameter, uses more than one method for including an access
         token, or is otherwise malformed.  The resource server SHOULD
         respond with the HTTP 400 (Bad Request) status code.

   invalid_token
         The access token provided is expired, revoked, malformed, or
         invalid for other reasons.  The resource SHOULD respond with
         the HTTP 401 (Unauthorized) status code.  The client MAY
         request a new access token and retry the protected resource
         request.

   insufficient_scope
         The request requires higher privileges than provided by the
         access token.  The resource server SHOULD respond with the HTTP
         403 (Forbidden) status code and MAY include the "scope"
         attribute with the scope necessary to access the protected
         resource.




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   If the request lacks any authentication information (i.e. the client
   was unaware authentication is necessary or attempted using an
   unsupported authentication method), the resource server SHOULD NOT
   include an error code or other error information.

   For example:

   HTTP/1.1 401 Unauthorized
   WWW-Authenticate: Bearer realm="example"


3.  Security Considerations

   This section describes the relevant security threats regarding token
   handling when using bearer tokens and describes how to mitigate these
   threats.

3.1.  Security Threats

   The following list presents several common threats against protocols
   utilizing some form of tokens.  This list of threats is based on NIST
   Special Publication 800-63 [NIST800-63].  Since this document builds
   on the OAuth 2.0 specification, we exclude a discussion of threats
   that are described there or in related documents.

   Token manufacture/modification:  An attacker may generate a bogus
      token or modify the token contents (such as the authentication or
      attribute statements) of an existing token, causing the resource
      server to grant inappropriate access to the client.  For example,
      an attacker may modify the token to extend the validity period; a
      malicious client may modify the assertion to gain access to
      information that they should not be able to view.

   Token disclosure:  Tokens may contain authentication and attribute
      statements that include sensitive information.

   Token redirect:  An attacker uses a token generated for consumption
      by a particular resource server to gain access to a different
      resource server that mistakenly believes the token to be for it.

   Token replay:  An attacker attempts to use a token that has already
      been used with that resource server in the past.

3.2.  Threat Mitigation

   A large range of threats can be mitigated by protecting the contents
   of the token by using a digital signature or a Message Authentication
   Code (MAC).  Alternatively, a bearer token can contain a reference to



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   authorization information, rather than encoding the information
   directly.  Such references MUST be infeasible for an attacker to
   guess; using a reference may require an extra interaction between a
   server and the token issuer to resolve the reference to the
   authorization information.  The mechanics of such an interaction are
   not defined by this specification.

   This document does not specify the encoding or the contents of the
   token; hence detailed recommendations for token integrity protection
   are outside the scope of this document.  We assume that the token
   integrity protection is sufficient to prevent the token from being
   modified.

   To deal with token redirect, it is important for the authorization
   server to include the identity of the intended recipients (the
   audience), typically a single resource server (or a list of resource
   servers), in the token.  Restricting the use of the token to a
   specific scope is also recommended.

   To provide protection against token disclosure, confidentiality
   protection is applied via TLS [RFC5246] with a ciphersuite that
   offers confidentiality protection.  This requires that the
   communication interaction between the client and the authorization
   server, as well as the interaction between the client and the
   resource server, utilize confidentiality protection.  Since TLS is
   mandatory to implement and to use with this specification, it is the
   preferred approach for preventing token disclosure via the
   communication channel.  For those cases where the client is prevented
   from observing the contents of the token, token encryption MUST be
   applied in addition to the usage of TLS protection.

   To deal with token capture and replay, the following recommendations
   are made: First, the lifetime of the token has to be limited by
   putting a validity time field inside the protected part of the token.
   Note that using short-lived (one hour or less) tokens reduces the
   impact of one of them being leaked.  Second, confidentiality
   protection of the exchanges between the client and the authorization
   server and between the client and the resource server MUST be
   applied, for instance, through the use of TLS [RFC5246].  As a
   consequence, no eavesdropper along the communication path is able to
   observe the token exchange.  Consequently, such an on-path adversary
   cannot replay the token.  Furthermore, when presenting the token to a
   resource server, the client MUST verify the identity of that resource
   server, as per [RFC2818].  Note that the client MUST validate the TLS
   certificate chain when making these requests to protected resources.
   Presenting the token to an unauthenticated and unauthorized resource
   server or failing to validate the certificate chain will allow
   adversaries to steal the token and gain unauthorized access to



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   protected resources.

3.3.  Summary of Recommendations

   Safeguard bearer tokens  Client implementations MUST ensure that
      bearer tokens are not leaked to unintended parties, as they will
      be able to use them to gain access to protected resources.  This
      is the primary security consideration when using bearer tokens and
      underlies all the more specific recommendations that follow.

   Validate SSL certificate chains  The client MUST validate the TLS
      certificate chain when making requests to protected resources.
      Failing to do so may enable DNS hijacking attacks to steal the
      token and gain unintended access.

   Always use TLS (https)  Clients MUST always use TLS [RFC5246] (https)
      or equivalent transport security when making requests with bearer
      tokens.  Failing to do so exposes the token to numerous attacks
      that could give attackers unintended access.

   Don't store bearer tokens in cookies  Implementations MUST NOT store
      bearer tokens within cookies that can be sent in the clear (which
      is the default transmission mode for cookies).  Implementations
      that do store bearer tokens in cookies MUST take precautions
      against cross site request forgery.

   Issue short-lived bearer tokens  Using short-lived (one hour or less)
      bearer tokens can reduce the impact of one of them being leaked.
      In particular, only short-lived bearer tokens should be issued to
      clients that run within a web browser or other environments where
      information leakage may occur.

   Issue scoped bearer tokens  Issue bearer tokens that contain an
      audience restriction, scoping their use to the intended relying
      party or set of relying parties.

   Don't pass bearer tokens in page URLs  Browsers, web servers, and
      other software may not adequately secure URLs in the browser
      history, web server logs, and other data structures.  If bearer
      tokens are passed in page URLs (typically as query string
      parameters), attackers might be able to steal them from the
      history data, logs, or other unsecured locations.  Instead, pass
      bearer tokens in HTTP message headers or message bodies for which
      confidentiality measures are taken.







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4.  IANA Considerations

4.1.  OAuth Access Token Type Registration

   This specification registers the following access token type in the
   OAuth Access Token Type Registry.

4.1.1.  The "Bearer" OAuth Access Token Type

   Type name:
      Bearer

   Additional Token Endpoint Response Parameters:
      (none)

   HTTP Authentication Scheme(s):
      Bearer

   Change controller:
      IETF

   Specification document(s):
      [[ this document ]]

4.2.  Authentication Scheme Registration

   This specification registers the following authentication scheme in
   the Authentication Scheme Registry defined in
   [I-D.ietf-httpbis-p7-auth].

4.2.1.  The "Bearer" Authentication Scheme

   Authentication Scheme Name:
      Bearer

   Pointer to specification text:
      [[ this document ]]

   Notes (optional):
      (none)


5.  References

5.1.  Normative References

   [I-D.ietf-httpbis-p1-messaging]
              Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,



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              Masinter, L., Leach, P., Berners-Lee, T., Reschke, J., and
              Y. Lafon, "HTTP/1.1, part 1: URIs, Connections, and
              Message Parsing", draft-ietf-httpbis-p1-messaging-16 (work
              in progress), August 2011.

   [I-D.ietf-httpbis-p7-auth]
              Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Reschke, J., and
              Y. Lafon, "HTTP/1.1, part 7: Authentication",
              draft-ietf-httpbis-p7-auth-16 (work in progress),
              August 2011.

   [I-D.ietf-oauth-v2]
              Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
              2.0 Authorization Protocol", draft-ietf-oauth-v2-22 (work
              in progress), September 2011.

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [W3C.REC-html401-19991224]
              Raggett, D., Jacobs, I., and A. Hors, "HTML 4.01
              Specification", World Wide Web Consortium
              Recommendation REC-html401-19991224, December 1999,
              <http://www.w3.org/TR/1999/REC-html401-19991224>.

5.2.  Informative References

   [NIST800-63]
              Burr, W., Dodson, D., Perlner, R., Polk, T., Gupta, S.,
              and E. Nabbus, "NIST Special Publication 800-63-1,
              INFORMATION SECURITY", December 2008.



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   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.


Appendix A.  Acknowledgements

   The following people contributed to preliminary versions of this
   document: Blaine Cook (BT), Brian Eaton (Google), Yaron Y. Goland
   (Microsoft), Brent Goldman (Facebook), Raffi Krikorian (Twitter),
   Luke Shepard (Facebook), and Allen Tom (Yahoo!).  The content and
   concepts within are a product of the OAuth community, the WRAP
   community, and the OAuth Working Group.

   The OAuth Working Group has dozens of very active contributors who
   proposed ideas and wording for this document, including: Michael
   Adams, Andrew Arnott, Dirk Balfanz, Brian Campbell, Leah Culver, Bill
   de hOra, Brian Ellin, Igor Faynberg, George Fletcher, Tim Freeman,
   Evan Gilbert, Justin Hart, John Kemp, Eran Hammer-Lahav, Chasen Le
   Hara, Michael B. Jones, Torsten Lodderstedt, Eve Maler, James Manger,
   Laurence Miao, Chuck Mortimore, Anthony Nadalin, Justin Richer, Peter
   Saint-Andre, Nat Sakimura, Rob Sayre, Marius Scurtescu, Naitik Shah,
   Justin Smith, Jeremy Suriel, Christian Stuebner, Paul Tarjan, and
   Franklin Tse.


Appendix B.  Document History

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

   -09

   o  Incorporated working group last call comments.  Specific changes
      were:

   o  Use definitions from [I-D.ietf-httpbis-p7-auth] rather than
      [RFC2617].

   o  Update credentials definition to conform to
      [I-D.ietf-httpbis-p7-auth].

   o  Further clarified that query parameters may occur in any order.

   o  Specify that error_description is UTF-8 encoded (matching the core
      specification).





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   o  Registered "Bearer" Authentication Scheme in Authentication Scheme
      Registry defined by [I-D.ietf-httpbis-p7-auth].

   o  Updated references to oauth-v2, httpbis-p1-messaging, and httpbis-
      p7-auth drafts.

   o  Other wording improvements not introducing normative changes.

   -08

   o  Updated references to oauth-v2 and httpbis drafts.

   -07

   o  Added missing comma in error response example.

   -06

   o  Changed parameter name "bearer_token" to "access_token", per
      working group consensus.

   o  Changed HTTP status code for "invalid_request" error code from
      HTTP 401 (Unauthorized) back to HTTP 400 (Bad Request), per input
      from HTTP working group experts.

   -05

   o  Removed OAuth Errors Registry, per design team input.

   o  Changed HTTP status code for "invalid_request" error code from
      HTTP 400 (Bad Request) to HTTP 401 (Unauthorized) to match HTTP
      usage [[ change pending working group consensus ]].

   o  Added missing quotation marks in error-uri definition.

   o  Added note to add language and encoding information to
      error_description if the core specification does.

   o  Explicitly reference the Augmented Backus-Naur Form (ABNF) defined
      in [RFC5234].

   o  Use auth-param instead of repeating its definition, which is (
      token "=" ( token / quoted-string ) ).

   o  Clarify security considerations about including an audience
      restriction in the token and include a recommendation to issue
      scoped bearer tokens in the summary of recommendations.




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   -04

   o  Edits responding to working group last call feedback on -03.
      Specific edits enumerated below.

   o  Added Bearer Token definition in Terminology section.

   o  Changed parameter name "oauth_token" to "bearer_token".

   o  Added realm parameter to "WWW-Authenticate" response to comply
      with [RFC2617].

   o  Removed "[ RWS 1#auth-param ]" from "credentials" definition since
      it did not comply with the ABNF in [I-D.ietf-httpbis-p7-auth].

   o  Removed restriction that the "bearer_token" (formerly
      "oauth_token") parameter be the last parameter in the entity-body
      and the HTTP request URI query.

   o  Do not require WWW-Authenticate Response in a reply to a malformed
      request, as an HTTP 400 Bad Request response without a WWW-
      Authenticate header is likely the right response in some cases of
      malformed requests.

   o  Removed OAuth Parameters registry extension.

   o  Numerous editorial improvements suggested by working group
      members.

   -03

   o  Restored the WWW-Authenticate response header functionality
      deleted from the framework specification in draft 12 based upon
      the specification text from draft 11.

   o  Augmented the OAuth Parameters registry by adding two additional
      parameter usage locations: "resource request" and "resource
      response".

   o  Registered the "oauth_token" OAuth parameter with usage location
      "resource request".

   o  Registered the "error" OAuth parameter.

   o  Created the OAuth Error registry and registered errors.

   o  Changed the "OAuth2" OAuth access token type name to "Bearer".




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   -02

   o  Incorporated feedback received on draft 01.  Most changes were to
      the security considerations section.  No normative changes were
      made.  Specific changes included:

   o  Changed terminology from "token reuse" to "token capture and
      replay".

   o  Removed sentence "Encrypting the token contents is another
      alternative" from the security considerations since it was
      redundant and potentially confusing.

   o  Corrected some references to "resource server" to be
      "authorization server" in the security considerations.

   o  Generalized security considerations language about obtaining
      consent of the resource owner.

   o  Broadened scope of security considerations description for
      recommendation "Don't pass bearer tokens in page URLs".

   o  Removed unused reference to OAuth 1.0.

   o  Updated reference to framework specification and updated David
      Recordon's e-mail address.

   o  Removed security considerations text on authenticating clients.

   o  Registered the "OAuth2" OAuth access token type and "oauth_token"
      parameter.

   -01

   o  First public draft, which incorporates feedback received on -00
      including enhanced Security Considerations content.  This version
      is intended to accompany OAuth 2.0 draft 11.

   -00

   o  Initial draft based on preliminary version of OAuth 2.0 draft 11.










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Authors' Addresses

   Michael B. Jones
   Microsoft

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


   Dick Hardt
   independent

   Email: dick.hardt@gmail.com
   URI:   http://dickhardt.org/


   David Recordon
   Facebook

   Email: dr@fb.com
   URI:   http://www.davidrecordon.com/






























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