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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 RFC 6749

Network Working Group                               E. Hammer-Lahav, Ed.
Internet-Draft                                                    Yahoo!
Obsoletes: 5849 (if approved)                                D. Recordon
Intended status: Standards Track                                Facebook
Expires: January 12, 2011                                       D. Hardt
                                                               Microsoft
                                                           July 11, 2010


                         The OAuth 2.0 Protocol
                         draft-ietf-oauth-v2-10

Abstract

   This specification describes the OAuth 2.0 protocol.

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 12, 2011.

Copyright Notice

   Copyright (c) 2010 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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7
     1.4.  Client Profiles  . . . . . . . . . . . . . . . . . . . . . 10
       1.4.1.  Web Server . . . . . . . . . . . . . . . . . . . . . . 10
       1.4.2.  User-Agent . . . . . . . . . . . . . . . . . . . . . . 11
       1.4.3.  Native Application . . . . . . . . . . . . . . . . . . 13
       1.4.4.  Autonomous . . . . . . . . . . . . . . . . . . . . . . 14
   2.  Client Credentials . . . . . . . . . . . . . . . . . . . . . . 14
     2.1.  Client Password Credentials  . . . . . . . . . . . . . . . 15
   3.  Obtaining End-User Authorization . . . . . . . . . . . . . . . 16
     3.1.  Authorization Response . . . . . . . . . . . . . . . . . . 18
     3.2.  Error Response . . . . . . . . . . . . . . . . . . . . . . 20
       3.2.1.  Error Codes  . . . . . . . . . . . . . . . . . . . . . 21
   4.  Obtaining an Access Token  . . . . . . . . . . . . . . . . . . 21
     4.1.  Access Grant Types . . . . . . . . . . . . . . . . . . . . 23
       4.1.1.  Authorization Code . . . . . . . . . . . . . . . . . . 23
       4.1.2.  Resource Owner Password Credentials  . . . . . . . . . 24
       4.1.3.  Assertion  . . . . . . . . . . . . . . . . . . . . . . 24
       4.1.4.  Refresh Token  . . . . . . . . . . . . . . . . . . . . 25
     4.2.  Access Token Response  . . . . . . . . . . . . . . . . . . 26
     4.3.  Error Response . . . . . . . . . . . . . . . . . . . . . . 27
       4.3.1.  Error Codes  . . . . . . . . . . . . . . . . . . . . . 28
   5.  Accessing a Protected Resource . . . . . . . . . . . . . . . . 29
     5.1.  Authenticated Requests . . . . . . . . . . . . . . . . . . 29
       5.1.1.  The Authorization Request Header Field . . . . . . . . 30
       5.1.2.  URI Query Parameter  . . . . . . . . . . . . . . . . . 30
       5.1.3.  Form-Encoded Body Parameter  . . . . . . . . . . . . . 31
     5.2.  The WWW-Authenticate Response Header Field . . . . . . . . 32
       5.2.1.  Error Codes  . . . . . . . . . . . . . . . . . . . . . 33
   6.  Extensibility  . . . . . . . . . . . . . . . . . . . . . . . . 34
     6.1.  Defining New Client Credentials Types  . . . . . . . . . . 34
     6.2.  Defining New Endpoint Parameters . . . . . . . . . . . . . 34
     6.3.  Defining New Header Field Parameters . . . . . . . . . . . 35
     6.4.  Defining New Access Grant Types  . . . . . . . . . . . . . 35
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 35
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 35
     8.1.  The OAuth Parameters Registry  . . . . . . . . . . . . . . 35
       8.1.1.  Registration Template  . . . . . . . . . . . . . . . . 36
       8.1.2.  Example  . . . . . . . . . . . . . . . . . . . . . . . 36
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . . 37
   Appendix B.  Contributors  . . . . . . . . . . . . . . . . . . . . 37
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 37
   Appendix D.  Document History  . . . . . . . . . . . . . . . . . . 38
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 42



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     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 42
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 43
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43
















































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1.  Introduction

   With the increasing use of distributed web services and cloud
   computing, third-party applications require access to server-hosted
   resources.  These resources are usually protected and require
   authentication using the resource owner's credentials (typically a
   username and password).

   In the traditional client-server authentication model, the client
   accesses a protected resource on the server by authenticating with
   the server using the resource owner's credentials.  In order to
   provide third-party applications access to protected resources, the
   resource owner shares its credentials with the third-party.  This
   creates several problems and limitations:

   o  Third-party applications are required to store the resource-
      owner's credentials for future use, typically a password in clear-
      text.

   o  Servers are required to support password (symmetric)
      authentication, despite the security weaknesses created by
      passwords.

   o  Third-party applications gain overly broad access to the resource-
      owner's protected resources, leaving resource owners without any
      ability to restrict access to a limited subset of resources, to
      limit access duration, or to limit access to the methods supported
      by these resources.

   o  Resource owners cannot revoke access to an individual third-party
      without revoking access to all third-parties, and must do so by
      changing their password.

   OAuth address these issues by separating the role of the client from
   that of the resource owner.  In OAuth, the client (which is usually
   not the resource owner, but is acting on the resource owner's behalf)
   requests access to resources controlled by the resource owner and
   hosted by the resource server, and is issued a different set of
   credentials than those of the resource owner.

   Instead of using the resource owner's credentials to access protected
   resources, clients obtain an access token (a string which denotes a
   specific scope, duration, and other attributes).  The format and
   structure of access tokens is beyond the scope of this specification.

   Tokens are issued to third-party 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



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   server.  The interaction between the authorization server and
   resource server is beyond the scope of this specification.

   For example, a web user (resource owner) can grant a printing service
   (client) access to her protected photos stored at a photo sharing
   service (resource server), without sharing her username and password
   with the printing service.  Instead, she authenticates directly with
   an authentication service trusted by the photo sharing service
   (authorization server) which issues the printing service delegation-
   specific credentials (token).

   This specification defines the use of OAuth over HTTP [RFC2616] (or
   HTTP over TLS as defined by [RFC2818]).  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].  Additionally, the following rules
   are included from [RFC2617]: realm, auth-param; from [RFC3986]: URI-
   Reference; and from [I-D.ietf-httpbis-p1-messaging]: OWS, RWS, and
   quoted-string.

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

1.2.  Terminology

   protected resource
         An access-restricted resource which can be obtained using an
         OAuth-authenticated request.

   resource server
         A server capable of accepting and responding to protected
         resource requests.

   client
         An application obtaining authorization and making protected
         resource requests.

   resource owner
         An entity capable of granting access to a protected resource.





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   end-user
         A human resource owner.

   token
         A string representing an access authorization issued to the
         client.  The string is usually opaque to the client.  Tokens
         represent specific scopes and durations of access, granted by
         the resource owner, and enforced by the resource server and
         authorization servers.  The token may denote an identifier used
         to retrieve the authorization information, or self-contain the
         authorization information in a verifiable manner (i.e. a token
         string consisting of some data and a signature).  Tokens may be
         pure capabilities.  Specific additional authentication
         credentials may be required in order for a client to use a
         token.

   access token
         A token used by the client to make authenticated requests on
         behalf of the resource owner.

   refresh token
         A token used by the client to obtain a new access token without
         having to involve the resource owner.

   authorization code  A short-lived token representing the access grant
         provided by the end-user.  The authorization code is used to
         obtain an access token and a refresh token.

   authorization server
         A server capable of issuing tokens after successfully
         authenticating the resource owner and obtaining authorization.
         The authorization server may be the same server as the resource
         server, or a separate entity.

   end-user authorization endpoint
         The authorization server's HTTP endpoint capable of
         authenticating the end-user and obtaining authorization.  The
         end-user authorization endpoint is described in Section 3.

   token endpoint
         The authorization server's HTTP endpoint capable of issuing
         tokens and refreshing expired tokens.  The token endpoint is
         described in Section 4.

   client identifier
         A unique identifier issued to the client to identify itself to
         the authorization server.  Client identifiers may have a
         matching secret.  The client identifier is described in



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         Section 2.

1.3.  Overview

   OAuth provides a method for clients to access a protected resource on
   behalf of a resource owner.  Before a client can access a protected
   resource, it must first obtain authorization from the resource owner,
   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.


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


                     Figure 1: Abstract Protocol Flow

   The abstract flow illustrated in Figure 1 includes the following
   steps:

   (A)  The client requests authorization from the resource owner.  The
        client should not request the resource owner's credentials
        directly.  Instead, it should request authorization via an
        authorization server or other entities.  For example, the client
        directs the resource owner to the authorization server which in
        turn issues it an access grant.  When unavoidable, the client
        interacts directly with the end-user, asking for the end-user's
        username and password.  If the client is acting autonomously,
        the authorization request is beyond the scope of this
        specification.




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   (B)  The client is issued an access grant which represents the
        authorization provided by the resource owner.  The access grant
        can be expressed as:

        *  Authorization code - an access grant obtained via an
           authorization server.  Section 3 describes how to obtain an
           authorization code when the end-user is present and using a
           user-agent.

        *  Assertion - an access grant obtained using a different trust
           framework.  Assertions enable the client to utilize existing
           trust relationships to obtain an access token.  They provide
           a bridge between OAuth and other trust frameworks.  The
           access grant represented by an assertion depends on the
           assertion type, its content, and how it was issued, which are
           beyond the scope of this specification.

        *  Resource owner password credentials - obtained when
           interacting directly with a resource-owner.  Resource owner
           password credentials (i.e. a username and password) should
           only be used when there is a high degree of trust between the
           resource owner and the client (e.g. its computer operating
           system or a highly privileged application).  However, unlike
           the HTTP Basic authentication scheme defined in [RFC2617],
           the resource owner's credentials are used for a single
           request and are exchanged for an access token and refresh
           token.  This eliminates the need for the client to store the
           resource-owner's credentials for future use.

   (C)  The client requests an access token by authenticating with the
        authorization server, and presenting the access grant.  The
        token request is described in Section 4.

   (D)  The authorization server validates the client credentials and
        the access grant, and issues an access token with an optional
        refresh token.  Access tokens usually have a shorter lifetime
        than the access grant.  Refresh tokens usually have a lifetime
        equal to the duration of the access grant.  When an access token
        expires, the refresh token is used to obtain a new access token
        without having to request another access grant from the resource
        owner.

   (E)  The client makes a protected resource request to the resource
        server, and presents the access token in order to gain access.
        Accessing a protected resource is described in Section 5.






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

   When the client is acting on its own behalf (the client is also the
   resource owner), the client does not obtain an access grant.  The
   simplified protocol flow is illustrated in Figure 2:


     +--------+                                  +---------------+
     |        |--(C)--- Client Credentials ----->| Authorization |
     |        |                                  |     Server    |
     |        |<-(D)------ Access Token ---------|               |
     |        |                                  +---------------+
     | Client |
     |        |                                  +---------------+
     |        |--(E)------ Access Token -------->|    Resource   |
     |        |                                  |     Server    |
     |        |<-(F)---- Protected Resource -----|               |
     +--------+                                  +---------------+


        Figure 2: Protocol Flow for Client Acting On Its Own Behalf

   When the client uses the user-agent profile (described in
   Section 1.4.2), the authorization request results in an access token,
   as illustrated in Figure 3:


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


               Figure 3: Indirect Access Grant Protocol Flow








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1.4.  Client Profiles

   OAuth supports a wide range of client types by providing a rich and
   extensible framework for establishing authorization and exchanging it
   for an access token.  The methods detailed in this specification were
   designed to accommodate four client types: web servers, user-agents,
   native applications, and autonomous clients.  Additional
   authorization flows and client profiles may be defined by other
   specifications to cover additional scenarios and client types.

1.4.1.  Web Server

   The web server profile is suitable for clients capable of interacting
   with the end-user's user-agent (typically a web browser) and capable
   of receiving incoming requests from the authorization server (capable
   of acting as an HTTP server).


     +----------+          Client Identifier      +---------------+
     |         -+----(A)--- & Redirect URI ------>|               |
     | End-user |                                 | Authorization |
     |    at    |<---(B)-- User authenticates --->|     Server    |
     | Browser  |                                 |               |
     |         -+----(C)-- Authorization Code ---<|               |
     +-|----|---+                                 +---------------+
       |    |                                         ^      v
      (A)  (C)                                        |      |
       |    |                                         |      |
       ^    v                                         |      |
     +---------+                                      |      |
     |         |>---(D)-- Client Credentials, --------'      |
     |   Web   |          Authorization Code,                |
     |  Client |            & Redirect URI                   |
     |         |                                             |
     |         |<---(E)----- Access Token -------------------'
     +---------+       (w/ Optional Refresh Token)


                         Figure 4: Web Server Flow

   The web server flow illustrated in Figure 4 includes the following
   steps:

   (A)  The web client initiates the flow by redirecting the end-user's
        user-agent to the end-user authorization endpoint as described
        in Section 3.  The client includes its client identifier,
        requested scope, local state, and a redirect URI to which the
        authorization server will send the end-user back once access is



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        granted (or denied).

   (B)  The authorization server authenticates the end-user (via the
        user-agent) and establishes whether the end-user grants or
        denies the client's access request.

   (C)  Assuming the end-user granted access, the authorization server
        redirects the user-agent back to the client to the redirection
        URI provided earlier.  The authorization includes an
        authorization code for the client to use to obtain an access
        token.

   (D)  The client requests an access token from the authorization
        server by authenticating and including the authorization code
        received in the previous step as described in Section 4.

   (E)  The authorization server validates the client credentials and
        the authorization code and responds back with the access token.

1.4.2.  User-Agent

   The user-agent profile is suitable for client applications residing
   in a user-agent, typically implemented in a browser using a scripting
   language such as JavaScript.  These clients cannot keep client
   secrets confidential and the authentication of the client is based on
   the user-agent's same-origin policy.

   Unlike other profiles in which the client makes separate requests for
   end-user authorization and access token, the client receives the
   access token as a result of the end-user authorization request in the
   form of an HTTP redirection.  The client requests the authorization
   server to redirect the user-agent to another web server or local
   resource accessible to the user-agent which is capable of extracting
   the access token from the response and passing it to the client.

   This user-agent profile does not utilize the client secret since the
   client executables reside on the end-user's computer or device which
   makes the client secret accessible and exploitable.  Because the
   access token is encoded into the redirection URI, it may be exposed
   to the end-user and other applications residing on the computer or
   device.










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          +----------+          Client Identifier     +----------------+
          |          |>---(A)-- & Redirection URI --->|                |
          |          |                                |                |
   End <--+  -  -  - +----(B)-- User authenticates -->|  Authorization |
   User   |          |                                |     Server     |
          |          |<---(C)--- Redirect URI -------<|                |
          |  Client  |         with Access Token      |                |
          |    in    |            in Fragment         +----------------+
          |  Browser |
          |          |                                +----------------+
          |          |>---(D)--- Redirect URI ------->|                |
          |          |         without Fragment       |   Web Server   |
          |          |                                |   with Client  |
          |    (F)   |<---(E)--- Web Page with ------<|    Resource    |
          |  Access  |              Script            |                |
          |   Token  |                                +----------------+
          +----------+


                         Figure 5: User-Agent Flow

   The user-agent flow illustrated in Figure 5 includes the following
   steps:

   (A)  The client sends the user-agent to the end-user authorization
        endpoint as described in Section 3.  The client includes its
        client identifier, requested scope, local state, and a redirect
        URI to which the authorization server will send the end-user
        back once authorization is granted (or denied).

   (B)  The authorization server authenticates the end-user (via the
        user-agent) and establishes whether the end-user grants or
        denies the client's access request.

   (C)  If the end-user granted access, the authorization server
        redirects the user-agent to the redirection URI provided
        earlier.  The redirection URI includes the access token in the
        URI fragment.

   (D)  The user-agent follows the redirection instructions by making a
        request to the web server which does not include the fragment.
        The user-agent retains the fragment information locally.

   (E)  The web server returns a web page (typically an HTML page with
        an embedded script) capable of accessing the full redirection
        URI including the fragment retained by the user-agent, and
        extracting the access token (and other parameters) contained in
        the fragment.



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   (F)  The user-agent executes the script provided by the web server
        locally, which extracts the access token and passes it to the
        client.

1.4.3.  Native Application

   Native application are clients running as native code on the end-
   user's computer or device (i.e. executing outside a user-agent or as
   a desktop program).  These clients are often capable of interacting
   with (or embedding) the end-user's user-agent but are limited in how
   such interaction affects their end-user experience.  In many cases,
   native applications are incapable of receiving direct callback
   requests from the server (e.g. firewall, operating system
   restrictions).

   Native application clients can be implemented in different ways based
   on their requirements and desired end-user experience.  Native
   application clients can:

   o  Utilize the end-user authorization endpoint as described in
      Section 3 by launching an external user-agent.  The client can
      capture the response by providing a redirection URI with a custom
      URI scheme (registered with the operating system to invoke the
      client application), or by providing a redirection URI pointing to
      a server-hosted resource under the client's control which makes
      the response available to the client (e.g. using the window title
      or other locations accessible from outside the user-agent).

   o  Utilize the end-user authorization endpoint as described in
      Section 3 by using an embedded user-agent.  The client obtains the
      response by directly communicating with the embedded user-agent.

   o  Prompt end-users for their password and use them directly to
      obtain an access token.  This is generally discouraged, as it
      hands the end-user's password directly to the third-party client
      which in turn has to store it in clear-text.  It also requires the
      server to support password-based authentication.

   When choosing between launching an external browser and an embedded
   user-agent, developers should consider the following:

   o  External user-agents may improve completion rate as the end-user
      may already be logged-in and not have to re-authenticate.

   o  Embedded user-agents often offer a better end-user flow, as they
      remove the need to switch context and open new windows.





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   o  Embedded user-agents pose a security challenge because users are
      authenticating in an unidentified window without access to the
      visual protections offered by many user-agents.

1.4.4.  Autonomous

   Autonomous clients utilize an existing trust relationship or
   framework to establish authorization.  Autonomous clients can be
   implemented in different ways based on their requirements and the
   existing trust framework they rely upon.  Autonomous clients can:

   o  Obtain an access token by authenticating with the authorization
      server using their client credentials.  The scope of the access
      token is limited to the protected resources under the control of
      the client, or that of another resource owner previously arranged
      with the authorization server.

   o  Use an existing access grant expressed as an assertion using an
      assertion format supported by the authorization server.  Using
      assertions requires the client to obtain a assertion (such as a
      SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
      or to self-issue an assertion.  The assertion format, the process
      by which the assertion is obtained, and the method of validating
      the assertion are defined by the assertion issuer and the
      authorization server, and are beyond the scope of this
      specification.


2.  Client Credentials

   When interacting with the authorization server, the client identifies
   itself using a client identifier and authenticates using a set of
   client credentials.  This specification provides one mechanism for
   authenticating the client using password credentials.

   The means through which the client obtains its credentials are beyond
   the scope of this specification, but usually involve registration
   with the authorization server. [[ OAuth Discovery provides one way of
   obtaining a client password ]]

   Due to the nature of some clients, authorization servers SHOULD NOT
   make assumptions about the confidentiality of client secrets without
   establishing trust with the client operator.  Authorization servers
   SHOULD NOT issue client secrets to clients incapable of keeping their
   secrets confidential.

   The authorization server MAY authenticate the client using any
   appropriate set of credentials and authentication scheme.  The client



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   MUST NOT utilize more than one set of credentials or authentication
   mechanism with each request.

2.1.  Client Password Credentials

   The client password credentials use a shared symmetric secret to
   authenticate the client.  The client identifier and password are
   included in the request using the HTTP Basic authentication scheme as
   defined in [RFC2617] by including the client identifier as the
   username and client password as the password.

   For example (line breaks are for display purposes only):


     POST /token HTTP/1.1
     Host: server.example.com
     Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
     Content-Type: application/x-www-form-urlencoded

     grant_type=authorization_code&client_id=s6BhdRkqt3&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb


   Alternatively, the client MAY include the password in the request
   body using the following parameter:

   client_secret  REQUIRED.  The client password.

   For example (line breaks are for display purposes only):


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

     grant_type=authorization_code&client_id=s6BhdRkqt3&
     client_secret=gX1fBat3bV&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb


   The authorization server MUST accept the client credentials using
   both the request parameter, and the HTTP Basic authentication scheme.
   The authorization server MAY support additional authentication
   schemes suitable for the transmission of a password.







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3.  Obtaining End-User Authorization

   When the client interacts with an end-user, the end-user MUST first
   grant the client authorization to access its protected resources.
   Once obtained, the end-user access grant is expressed as an
   authorization code which the client uses to obtain an access token.
   To obtain an end-user authorization, the client sends the end-user to
   the end-user authorization endpoint.

   At the end-user authorization endpoint, the end-user first
   authenticates with the authorization server, and then grants or
   denies the access request.  The way in which the authorization server
   authenticates the end-user (e.g. username and password login, OpenID,
   session cookies) and in which the authorization server obtains the
   end-user's authorization, including whether it uses a secure channel
   such as TLS, is beyond the scope of this specification.  However, the
   authorization server MUST first verify the identity of the end-user.

   The location of the end-user authorization endpoint can be found in
   the service documentation, or can be obtained by using [[ OAuth
   Discovery ]].  The end-user authorization endpoint URI MAY include a
   query component as defined by [RFC3986] section 3, which must be
   retained when adding additional query parameters.

   Since requests to the end-user authorization endpoint result in user
   authentication and the transmission of sensitive information, the
   authorization server SHOULD require the use of a transport-layer
   security mechanism such as TLS when sending requests to the end-user
   authorization endpoint.

   In order to direct the end-user's user-agent to the authorization
   server, the client constructs the request URI by adding the following
   parameters to the end-user authorization endpoint URI query component
   using the "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224]:

   response_type
         REQUIRED.  The requested response: an access token, an
         authorization code, or both.  The parameter value MUST be set
         to "token" for requesting an access token, "code" for
         requesting an authorization code, or "code_and_token" to
         request both.  The authorization server MAY decline to provide
         one or more of these response types. [[ The 'code_and_token'
         type is pending use cases and may be removed for the
         specification ]]






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   client_id
         REQUIRED.  The client identifier as described in Section 2.

   redirect_uri
         REQUIRED, unless a redirection URI has been established between
         the client and authorization server via other means.  An
         absolute URI to which the authorization server will redirect
         the user-agent to when the end-user authorization step is
         completed.  The authorization server SHOULD require the client
         to pre-register their redirection URI.

   scope
         OPTIONAL.  The scope of the access request expressed as a list
         of space-delimited strings.  The value of the "scope" parameter
         is defined by the authorization server.  If the value contains
         multiple space-delimited strings, their order does not matter,
         and each string adds an additional access range to the
         requested scope.

   state
         OPTIONAL.  An opaque value used by the client to maintain state
         between the request and callback.  The authorization server
         includes this value when redirecting the user-agent back to the
         client.

   The client directs the end-user to the constructed URI using an HTTP
   redirection response, or by other means available to it via the end-
   user's user-agent.  The authorization server MUST support the use of
   the HTTP "GET" method for the end-user authorization endpoint, and
   MAY support the use of the "POST" method as well.

   For example, the client directs the end-user's user-agent to make the
   following HTTP request using transport-layer security (line breaks
   are for display purposes only):


     GET /authorize?response_type=code&client_id=s6BhdRkqt3&
         redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
     Host: server.example.com


   If the client has previously registered a redirection URI with the
   authorization server, the authorization server MUST verify that the
   redirection URI received matches the registered URI associated with
   the client identifier. [[ provide guidance on how to perform matching
   ]]

   Parameters sent without a value MUST be treated as if they were



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   omitted from the request.  The authorization server SHOULD ignore
   unrecognized request parameters.

   The authorization server validates the request to ensure all required
   parameters are present and valid.  If the request is invalid, the
   authorization server immediately redirects the user-agent back to the
   client using the redirection URI provided with the appropriate error
   code as described in Section 3.2.

   The authorization server authenticates the end-user and obtains an
   authorization decision (by asking the end-user or by establishing
   approval via other means).  When a decision has been established, the
   authorization server directs the end-user's user-agent to the
   provided client redirection URI using an HTTP redirection response,
   or by other means available to it via the end-user's user-agent.

3.1.  Authorization Response

   If the end-user grants the access request, the authorization server
   issues an access token, an authorization code, or both, and delivers
   them to the client by adding the following parameters to the
   redirection URI (as described below):

   code
         REQUIRED if the response type is "code" or "code_and_token",
         otherwise MUST NOT be included.  The authorization code
         generated by the authorization server.  The authorization code
         SHOULD expire shortly after it is issued.  The authorization
         server MUST invalidate the authorization code after a single
         usage.  The authorization code is bound to the client
         identifier and redirection URI.

   access_token
         REQUIRED if the response type is "token" or "code_and_token",
         otherwise MUST NOT be included.  The access token issued by the
         authorization server.  The access token string MUST comply with
         the access-token rule defined in Section 5.1.1.

   expires_in
         OPTIONAL.  The duration in seconds of the access token lifetime
         if an access token is included.  For example, the value "3600"
         denotes that the access token will expire in one hour from the
         time the response was generated by the authorization server.

   scope
         OPTIONAL.  The scope of the access token as a list of space-
         delimited strings if an access token is included.  The value of
         the "scope" parameter is defined by the authorization server.



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         If the value contains multiple space-delimited strings, their
         order does not matter, and each string adds an additional
         access range to the requested scope.  The authorization server
         SHOULD include the parameter if the requested scope is
         different from the one requested by the client.

   state
         REQUIRED if the "state" parameter was present in the client
         authorization request.  Set to the exact value received from
         the client.

   The method in which the authorization server adds the parameter to
   the redirection URI is determined by the response type requested by
   the client in the authorization request using the "response_type"
   parameter.

   If the response type is "code", the authorization server adds the
   parameters to the redirection URI query component using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224].

   For example, the authorization server redirects the end-user's user-
   agent by sending the following HTTP response:


     HTTP/1.1 302 Found
     Location: https://client.example.com/cb?code=i1WsRn1uB1


   If the response type is "token", the authorization server adds the
   parameters to the redirection URI fragment component using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224].

   For example, the authorization server redirects the end-user's user-
   agent by sending the following HTTP response:


    HTTP/1.1 302 Found
    Location: http://example.com/rd#access_token=FJQbwq9&expires_in=3600


   If the response type is "code_and_token", the authorization server
   adds the "code" and "state" parameters to the redirection URI query
   component and the "access_token", "scope", and "expires_in" to the
   redirection URI fragment using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224].



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   For example, the authorization server redirects the end-user's user-
   agent by sending the following HTTP response (line breaks are for
   display purposes only):


     HTTP/1.1 302 Found
     Location: http://example.com/rd?code=i1WsRn1uB1
               #access_token=FJQbwq9&expires_in=3600


   Clients SHOULD ignore unrecognized response parameters.  The sizes of
   tokens and other values received from the authorization server, are
   left undefined by this specification.  Clients should avoid making
   assumptions about value sizes.  Servers should document the expected
   size of any value they issue.

3.2.  Error Response

   If the end-user denies the access request or if the request is
   invalid, the authorization server informs the client by adding the
   following parameters to the redirection URI query component using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224]:

   error
         REQUIRED.  A single error code as described in Section 3.2.1.

   error_description  OPTIONAL.  A human-readable text providing
         additional information, used to assist in the understanding and
         resolution of the error occurred.

   error_uri  OPTIONAL.  A URI identifying a human-readable web page
         with information about the error, used to provide the end-user
         with additional information about the error.

   state
         REQUIRED if the "state" parameter was present in the client
         authorization request.  Set to the exact value received from
         the client.

   For example, the authorization server redirects the end-user's user-
   agent by sending the following HTTP response:


     HTTP/1.1 302 Found
     Location: https://client.example.com/cb?error=access-denied





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3.2.1.  Error Codes

   The authorization server includes one of the following error codes
   with the error response:

   invalid_request
         The request is missing a required parameter, includes an
         unsupported parameter or parameter value, or is otherwise
         malformed.

   invalid_client
         The client identifier provided is invalid.

   unauthorized_client
         The client is not authorized to use the requested response
         type.

   redirect_uri_mismatch
         The redirection URI provided does not match a pre-registered
         value.

   access_denied
         The end-user or authorization server denied the request.

   unsupported_response_type
         The requested response type is not supported by the
         authorization server.

   invalid_scope
         The requested scope is invalid, unknown, or malformed.

   [[ Add mechanism for extending error codes ]]


4.  Obtaining an Access Token

   The client obtains an access token by authenticating with the
   authorization server and presenting its access grant (in the form of
   an authorization code, resource owner credentials, an assertion, or a
   refresh token).

   Since requests to the token endpoint result in the transmission of
   plain text credentials in the HTTP request and response, the
   authorization server MUST require the use of a transport-layer
   security mechanism when sending requests to the token endpoints.
   Servers MUST support TLS 1.2 as defined in [RFC5246], and MAY support
   additional transport-layer security mechanisms.




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   The client requests an access token by making an HTTP "POST" request
   to the token endpoint.  The location of the token endpoint can be
   found in the service documentation, or can be obtained by using [[
   OAuth Discovery ]].  The token endpoint URI MAY include a query
   component.

   The client authenticates with the authorization server by adding its
   client credentials to the request as described in Section 2.  The
   authorization server MAY allow unauthenticated access token requests
   when the client identity does not matter (e.g. anonymous client) or
   when the client identity is established via other means (e.g. using
   an assertion access grant).

   The client constructs the request by including the following
   parameters using the "application/x-www-form-urlencoded" format in
   the HTTP request entity-body:

   grant_type
         REQUIRED.  The access grant type included in the request.
         Value MUST be one of "authorization_code", "password",
         "assertion", "refresh_token", or "none".

   client_id
         REQUIRED, unless the client identity can be establish via other
         means (e.g. assertion).  The client identifier as described in
         Section 2.

   scope
         OPTIONAL.  The scope of the access request expressed as a list
         of space-delimited strings.  The value of the "scope" parameter
         is defined by the authorization server.  If the value contains
         multiple space-delimited strings, their order does not matter,
         and each string adds an additional access range to the
         requested scope.  If the access grant being used already
         represents an approved scope (e.g. authorization code,
         assertion), the requested scope MUST be equal or lesser than
         the scope previously granted.

   In addition, the client MUST include the appropriate parameters
   listed for the selected access grant type as described in
   Section 4.1.

   Parameters sent without a value MUST be treated as if they were
   omitted from the request.  The authorization server SHOULD ignore
   unrecognized request parameters.






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4.1.  Access Grant Types

   The client requests an access token using one of the four types of
   access grants: authorization code, password credentials, assertion,
   or refresh token.

   When requesting an access token using the "none" access grant type
   (no access grant is included), the client is requesting access to the
   protected resources under its control, or those of another resource
   owner which has been previously arranged with the authorization
   server (the method of which is beyond the scope of this
   specification).

4.1.1.  Authorization Code

   The client includes the authorization code using the
   "authorization_code" access grant type and the following parameters:

   code
         REQUIRED.  The authorization code received from the
         authorization server.

   redirect_uri
         REQUIRED.  The redirection URI used in the initial request.

   For example, the client makes the following HTTP request by including
   its client credentials via the "client_secret" parameter described in
   Section 2 and using transport-layer security (line breaks are for
   display purposes only):


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

     grant_type=authorization_code&client_id=s6BhdRkqt3&
     client_secret=gX1fBat3bV&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb


   The authorization server MUST:

   o  Validate the client credentials (if present) and ensure they match
      the authorization code.

   o  Verify that the authorization code and redirection URI are all
      valid and match its stored association.




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   If the request is valid, the authorization server issues a successful
   response as described in Section 4.2.

4.1.2.  Resource Owner Password Credentials

   The client includes the resource owner credentials using the
   "password" access grant type and the following parameters: [[ add
   internationalization consideration for username and password ]]

   username
         REQUIRED.  The resource owner's username.

   password
         REQUIRED.  The resource owner's password.

   For example, the client makes the following HTTP request by including
   its client credentials via the "client_secret" parameter described in
   Section 2 and using transport-layer security (line breaks are for
   display purposes only):


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

     grant_type=password&client_id=s6BhdRkqt3&
     client_secret=47HDu8s&username=johndoe&password=A3ddj3w


   The authorization server MUST validate the client credentials (if
   present) and end-user credentials and if valid issue an access token
   response as described in Section 4.2.

4.1.3.  Assertion

   The client includes the assertion using the "assertion" access grant
   type and the following parameters:

   assertion_type
         REQUIRED.  The format of the assertion as defined by the
         authorization server.  The value MUST be an absolute URI.

   assertion
         REQUIRED.  The assertion.







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   For example, the client makes the following HTTP request using
   transport-layer security, and client authentication is achieved via
   the assertion (line breaks are for display purposes only):


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

     grant_type=assertion&
     assertion_type=urn%3Aoasis%3Anames%3Atc%3ASAML%3A2.0%3Aassertion&
     assertion=PHNhbWxwOl...[omitted for brevity]...ZT4%3D


   The authorization server MUST validate the client credentials (if
   present) and the assertion and if valid issues an access token
   response as described in Section 4.2.  The authorization server
   SHOULD NOT issue a refresh token (instead, require the client to use
   the same or new assertion).

   Authorization servers SHOULD issue access tokens with a limited
   lifetime and require clients to refresh them by requesting a new
   access token using the same assertion if it is still valid.
   Otherwise the client MUST obtain a new valid assertion.

4.1.4.  Refresh Token

   The client includes the refresh token using the "refresh_token"
   access grant type and the following parameter:

   refresh_token
         REQUIRED.  The refresh token associated with the access token
         to be refreshed.

   For example, the client makes the following HTTP request by including
   its client credentials via the "client_secret" parameter described in
   Section 2 and using transport-layer security (line breaks are for
   display purposes only):


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

     grant_type=refresh_token&client_id=s6BhdRkqt3&
     client_secret=8eSEIpnqmM&refresh_token=n4E9O119d





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   The authorization server MUST verify the client credentials (if
   present), the validity of the refresh token, and that the resource
   owner's authorization is still valid.  If the request is valid, the
   authorization server issues an access token response as described in
   Section 4.2.  The authorization server MAY issue a new refresh token.

4.2.  Access Token Response

   After receiving and verifying a valid and authorized access token
   request from the client, the authorization server issues the access
   token and optional refresh token, and constructs the response by
   adding the following parameters to the entity body of the HTTP
   response with a 200 (OK) status code:

   The token response contains the following parameters:

   access_token
         REQUIRED.  The access token issued by the authorization server.
         The access token string MUST comply with the access-token rule
         defined in Section 5.1.1.

   expires_in
         OPTIONAL.  The duration in seconds of the access token
         lifetime.  For example, the value "3600" denotes that the
         access token will expire in one hour from the time the response
         was generated by the authorization server.

   refresh_token
         OPTIONAL.  The refresh token used to obtain new access tokens
         using the same end-user access grant as described in
         Section 4.1.4.  The authorization server SHOULD NOT issue a
         refresh token when the access grant type is set to "none".

   scope
         OPTIONAL.  The scope of the access token as a list of space-
         delimited strings.  The value of the "scope" parameter is
         defined by the authorization server.  If the value contains
         multiple space-delimited strings, their order does not matter,
         and each string adds an additional access range to the
         requested scope.  The authorization server SHOULD include the
         parameter if the requested scope is different from the one
         requested by the client.

   The parameters are including in the entity body of the HTTP response
   using the "application/json" media type as defined by [RFC4627].  The
   parameters are serialized into a JSON structure by adding each
   parameter at the highest structure level.  Parameter names and string
   values are included as JSON strings.  Numerical values are included



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   as JSON numbers.

   The authorization server MUST include the HTTP "Cache-Control"
   response header field with a value of "no-store" in any response
   containing tokens, secrets, or other sensitive information.

   For example:


     HTTP/1.1 200 OK
     Content-Type: application/json
     Cache-Control: no-store

     {
       "access_token":"SlAV32hkKG",
       "expires_in":3600,
       "refresh_token":"8xLOxBtZp8"
     }


   Clients SHOULD ignore unrecognized response parameters.  The sizes of
   tokens and other values received from the authorization server, are
   left undefined by this specification.  Clients should avoid making
   assumptions about value sizes.  Servers should document the expected
   size of any value they issue.

4.3.  Error Response

   If the token request is invalid or unauthorized, the authorization
   server constructs the response by adding the following parameter to
   the entity body of the HTTP response using the "application/json"
   media type:

   error
         REQUIRED.  A single error code as described in Section 4.3.1.

   error_description  OPTIONAL.  A human-readable text providing
         additional information, used to assist in the understanding and
         resolution of the error occurred.

   error_uri  OPTIONAL.  A URI identifying a human-readable web page
         with information about the error, used to provide the end-user
         with additional information about the error.








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   For example:


     HTTP/1.1 400 Bad Request
     Content-Type: application/json
     Cache-Control: no-store

     {
       "error":"invalid_request"
     }


   If the client provided invalid credentials using an HTTP
   authentication scheme via the "Authorization" request header field,
   the authorization server MUST respond with the HTTP 401
   (Unauthorized) status code.  Otherwise, the authorization server
   SHALL respond with the HTTP 400 (Bad Request) status code.

4.3.1.  Error Codes

   The authorization server includes one of the following error codes
   with the error response:

   invalid_request
         The request is missing a required parameter, includes an
         unsupported parameter or parameter value, repeats a parameter,
         includes multiple credentials, utilizes more than one mechanism
         for authenticating the client, or is otherwise malformed.

   invalid_client
         The client identifier provided is invalid, the client failed to
         authenticate, the client did not include its credentials,
         provided multiple client credentials, or used unsupported
         credentials type.

   unauthorized_client
         The authenticated client is not authorized to use the access
         grant type provided.

   invalid_grant
         The provided access grant is invalid, expired, or revoked (e.g.
         invalid assertion, expired authorization token, bad end-user
         password credentials, or mismatching authorization code and
         redirection URI).







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   unsupported_grant_type
         The access grant included - its type or another attribute - is
         not supported by the authorization server.

   invalid_scope
         The requested scope is invalid, unknown, malformed, or exceeds
         the previously granted scope.

   [[ Add mechanism for extending error codes ]]


5.  Accessing a Protected Resource

   Clients access protected resources by presenting an access token to
   the resource server.  Access tokens act as bearer tokens, where the
   token string acts as a shared symmetric secret.  This requires
   treating the access token with the same care as other secrets (e.g.
   end-user passwords).  Access tokens SHOULD NOT be sent in the clear
   over an insecure channel.

   However, when it is necessary to transmit access tokens in the clear
   without a secure channel, authorization servers SHOULD issue access
   tokens with limited scope and lifetime to reduce the potential risk
   from a compromised access token.

   Clients MUST NOT make authenticated requests with an access token to
   unfamiliar resource servers, regardless of the presence of a secure
   channel.

   The resource server MUST validate the access token and ensure it has
   not expired and that its scope covers the requested resource.  The
   methods used by the resource server to validate the access token are
   beyond the scope of this specification, but generally involve an
   interaction or coordination between the resource server and
   authorization server.

5.1.  Authenticated Requests

   Clients make authenticated token requests using the "Authorization"
   request header field.  Resource servers MUST accept authenticated
   requests using the "OAuth" HTTP authentication scheme as described in
   Section 5.1.1, and MAY support additional methods.

   Alternatively, clients MAY attempt to include the access token using
   the HTTP request URI in the query component as described in
   Section 5.1.2, or in the HTTP body when using the
   "application/x-www-form-urlencoded" content type as described in
   Section 5.1.3.  Resource server MAY support these alternative



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   methods.

   Clients SHOULD only use the request URI or body when the
   "Authorization" request header field is not available, and MUST NOT
   use more than one method in each request.

5.1.1.  The Authorization Request Header Field

   The "Authorization" request header field is used by clients to make
   authenticated token requests.  The client uses the "OAuth"
   authentication scheme to include the access token in the request.

   For example:


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


   The "Authorization" header field uses the framework defined by
   [RFC2617] as follows:


     credentials    = "OAuth" RWS access-token [ CS 1#auth-param ]
     access-token   = 1*( quoted-char / <"> )

     CS             = OWS "," OWS

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


      NOTE: [RFC5849] defines a different format for the "OAuth"
      authentication scheme.  Resource servers can differentiate between
      the two protocol versions based on the presence of the
      "oauth_signature_method" which is REQUIRED in the previous version
      and is not supported by this specification.

5.1.2.  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 "oauth_token" parameter.




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


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


   The HTTP request URI query can include other request-specific
   parameters, in which case, the "oauth_token" parameters SHOULD be
   appended following the request-specific parameters, properly
   separated by an "&" character (ASCII code 38).

   For example:


     http://example.com/resource?x=y&oauth_token=vF9dft4qmT


      NOTE: The "oauth_token" parameter is used by the previous version
      of the OAuth protocol as described in [RFC5849].  Resource servers
      can differentiate between the two protocol versions based on the
      presence of the "oauth_signature_method" which is REQUIRED in the
      previous version and is not supported by this specification.

5.1.3.  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
   "oauth_token" parameter.  The client can use this method only if the
   following REQUIRED conditions are met:

   o  The 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 "POST", "PUT", or "DELETE".

   The entity-body can include other request-specific parameters, in
   which case, the "oauth_token" parameters SHOULD be appended following
   the request-specific parameters, properly separated by an "&"
   character (ASCII code 38).




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   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

     oauth_token=vF9dft4qmT


      NOTE: The "oauth_token" parameter is used by the previous version
      of the OAuth protocol as described in [RFC5849].  Resource servers
      can differentiate between the two protocol versions based on the
      presence of the "oauth_signature_method" which is REQUIRED in the
      previous version and is not supported by this specification.

5.2.  The WWW-Authenticate Response Header Field

   If the protected resource request contains an invalid access token or
   is malformed, the resource server MUST include the HTTP
   "WWW-Authenticate" response header field.  The "WWW-Authenticate"
   header field uses the framework defined by [RFC2617] as follows:


     challenge       = "OAuth" RWS token-challenge

     token-challenge = realm
                       [ CS error ]
                       [ CS error-desc ]
                       [ CS error-uri ]
                       [ CS scope ]
                       [ CS 1#auth-param ]

     error           = "error" "=" <"> token <">
     error-desc      = "error_description" "=" quoted-string
     error-uri       = "error_uri" = <"> URI-Reference <">
     scope           = quoted-value /
                       <"> quoted-value *( 1*SP quoted-value ) <">
     quoted-value    = 1*quoted-char


   For example:


  HTTP/1.1 401 Unauthorized
  WWW-Authenticate: OAuth realm='Example Service', error='expired-token'




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   The "realm" attribute is used to provide the protected resources
   partition as defined by [RFC2617]. [[ add explanation ]]

   The "error" attribute is used to provide the client with the reason
   why the access request was declined.  The parameter values are
   described in Section 5.2.1.

   The "error_description" attribute provides a human-readable text
   containing additional information, used to assist in the
   understanding and resolution of the error occurred.

   The "error_uri" attribute provides a URI identifying a human-readable
   web page with information about the error, used to offer the end-user
   with additional information about the error.  If the value is not an
   absolute URI, it is relative to the URI of the requested protected
   resource.

   The "scope" attribute is a space-delimited list of scope values
   indicating the required scope of the access token for accessing the
   requested resource.

5.2.1.  Error Codes

   The authorization server includes one of the following error codes
   with the error 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 MUST
         respond with the HTTP 400 (Bad Request) status code.

   invalid_token
         The access token provided is invalid.  Resource servers SHOULD
         use this error code when receiving an expired token which
         cannot be refreshed to indicate to the client that a new
         authorization is necessary.  The resource server MUST respond
         with the HTTP 401 (Unauthorized) status code.

   expired_token
         The access token provided has expired.  Resource servers SHOULD
         only use this error code when the client is expected to be able
         to handle the response and request a new access token using the
         refresh token issued with the expired access token.  The
         resource server MUST respond with the HTTP 401 (Unauthorized)
         status code.




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   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.

   [[ Add mechanism for extending error codes ]]

   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: OAuth realm='Example Service'



6.  Extensibility

6.1.  Defining New Client Credentials Types

   [[ TBD ]]

6.2.  Defining New Endpoint Parameters

   Applications that wish to define new request or response parameters
   for use with the end-user authorization endpoint or the token
   endpoint SHALL do so in one of two ways: register them in the
   parameters registry (following the procedures in Section 8.1), or use
   the "x_" parameter name prefix.

   Parameters utilizing the "x_" parameter name prefix MUST be limited
   to vendor-specific extensions that are not commonly applicable, and
   are specific to the implementation details of the authorization
   server where they are used.  All other new parameters MUST be
   registered, and MUST NOT use the "x_" parameter name prefix.

   Parameter names MUST conform to the param-name ABNF, and parameter
   values syntax MUST be well-defined (e.g., using ABNF, or a reference
   to the syntax of an existing parameter).


     param-name  = 1*name-char



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     name-char   = "-" / "." / "_" / DIGIT / ALPHA


6.3.  Defining New Header Field Parameters

   Applications that wish to define new parameters for use in the OAuth
   "Authorization" or "WWW-Authenticate" header fields MUST register
   them in the parameters registry, following the procedures in
   Section 8.1.

   Parameter names MUST conform to the param-name ABNF and MUST NOT
   begin with "x_".  Parameter values MUST conform to the param-value
   ABNF and their syntax MUST be well-defined (e.g., using ABNF, or a
   reference to the syntax of an existing parameter).


     param-value  = quoted-value | quoted-string


6.4.  Defining New Access Grant Types

   The assertion access grant type was designed to allow the
   authorization server to accept additional access grants not
   specified.  Applications that wish to define additional access grant
   types can do so by utilizing a new or existing assertion type and
   format.


7.  Security Considerations

   [[ TBD ]]


8.  IANA Considerations

8.1.  The OAuth Parameters Registry

   This document establishes the OAuth parameters registry.

   Additional parameters to be use in the end-user authorization
   endpoint request, the end-user authorization endpoint response, the
   token endpoint request, the token endpoint response, the
   "Authorization" header field, or the "WWW-Authenticate" header field,
   are registered on the advice of one or more Designated Experts
   (appointed by the IESG or their delegate), with a Specification
   Required (using terminology from [RFC5226]).  However, to allow for
   the allocation of values prior to publication, the Designated
   Expert(s) may approve registration once they are satisfied that such



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   a specification will be published.

   Registration requests should be sent to the [TBD]@ietf.org mailing
   list for review and comment, with an appropriate subject (e.g.,
   "Request for parameter: example"). [[ Note to RFC-EDITOR: The name of
   the mailing list should be determined in consultation with the IESG
   and IANA.  Suggested name: oauth-ext-review. ]]

   Before a period of 14 days has passed, the Designated Expert(s) will
   either approve or deny the registration request, communicating this
   decision both to the review list and to IANA.  Denials should include
   an explanation and, if applicable, suggestions as to how to make the
   request successful.  Registration requests that are undetermined for
   a period longer than 21 days can be brought to the IESG's attention
   (using the iesg@iesg.org mailing list) for resolution.

8.1.1.  Registration Template

   Parameter name:  The name requested (e.g., "example").

   Parameter usage location:  The location(s) where parameter can be
      used.  The possible locations are: the end-user authorization
      endpoint request, the end-user authorization endpoint response,
      the token endpoint request, the token endpoint response, the
      "Authorization" header field, or the "WWW-Authenticate" header
      field.

   Change controller:  For standards-track RFCs, state "IETF".  For
      others, give the name of the responsible party.  Other details
      (e.g., postal address, e-mail address, home page URI) may also be
      included.

   Specification document(s):  Reference to document that specifies the
      parameter, preferably including a URI that can be used to retrieve
      a copy of the document.  An indication of the relevant sections
      may also be included, but is not required.

   Related information:  Optionally, citations to additional documents
      containing further relevant information.

8.1.2.  Example

   The following is the parameter registration request for the "scope"
   parameter as defined in this specification:







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   Parameter name:  scope

   Parameter usage location:  The end-user authorization endpoint
      request, the end-user authorization endpoint response, the token
      endpoint request, the token endpoint response, and the
      "WWW-Authenticate" header field.

   Change controller:  IETF

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

   Related information:  None


Appendix A.  Examples

   [[ TBD ]]


Appendix B.  Contributors

   The following people contributed to preliminary versions of this
   document: Blaine Cook (BT), Brian Eaton (Google), Yaron 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, 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: [[ If your
   name is missing or you think someone should be added here, please
   send Eran a note - don't be shy ]]

   Michael Adams, Andrew Arnott, Dirk Balfanz, Brian Campbell, Leah
   Culver, Brian Ellin, Igor Faynberg, George Fletcher, Evan Gilbert,
   Justin Hart, John Kemp, Chasen Le Hara, Torsten Lodderstedt, Eve
   Maler, James Manger, Laurence Miao, Chuck Mortimore, Justin Richer,
   Peter Saint-Andre, Nat Sakimura, Rob Sayre, Marius Scurtescu, Justin
   Smith, Jeremy Suriel, and Franklin Tse.


Appendix C.  Acknowledgements

   [[ Add OAuth 1.0a authors + WG contributors ]]







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Appendix D.  Document History

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

   -10

   o  Fixed typos.  Many editorial changes.  Rewrote introduction.
      removed terminology grouping.

   o  Allowed POST for end-user authorization endpoint.

   o  Fixed token endpoint to not require client authentication.

   o  Made URI query and POST body 'oauth_token' parameter optional.

   o  Moved all parameter names and values to use underscores.

   o  Changed 'basic_credentials' to 'password',
      'invalid_client_credentials' and 'invalid_client_id' to
      'invalid_client'.

   o  Added note that access token requests without an access grant
      should not include a refresh token.

   o  Changed scheme name from 'Token' to 'OAuth', simplified request
      format to simple string for token instead of key=value pair (still
      supported for extensions).

   o  Defined permitted access token string characters (suitable for
      inclusion in an HTTP header).

   o  Added a note about conflicts with previous versions.

   o  Moved 'client_id' definition from client authentication to access
      token endpoint.

   -09

   o  Fixed typos, editorial changes.

   o  Added token expiration example.

   o  Added scope parameter to end-user authorization endpoint response.

   o  Added note about parameters with empty values (same as omitted).

   o  Changed parameter values to use '-' instead of '_'.  Parameter
      names still use '_'.



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   o  Changed authorization endpoint client type to response type with
      values: code, token, and both.

   o  Complete cleanup of error codes.  Added support for error
      description and URI.

   o  Add initial extensibility support.

   -08

   o  Renamed verification code to authorization code.

   o  Revised terminology, structured section, added new terms.

   o  Changed flows to profiles and moved to introduction.

   o  Added support for access token rescoping.

   o  Cleaned up client credentials section.

   o  New introduction overview.

   o  Added error code for invalid username and password, and renamed
      error code to be more consistent.

   o  Added access grant type parameter to token endpoint.

   -07

   o  Major rewrite of entire document structure.

   o  Removed device profile.

   o  Added verification code support to user-agent flow.

   o  Removed multiple formats support, leaving JSON as the only format.

   o  Changed assertion "assertion_format" parameter to
      "assertion_type".

   o  Removed "type" parameter from token endpoint.

   -06

   o  Editorial changes, corrections, clarifications, etc.

   o  Removed conformance section.




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   o  Moved authors section to contributors appendix.

   o  Added section on native applications.

   o  Changed error response to use the requested format.  Added support
      for HTTP "Accept" header.

   o  Flipped the order of the web server and user-agent flows.

   o  Renamed assertion flow "format" parameter name to
      "assertion_format" to resolve conflict.

   o  Removed the term identifier from token definitions.  Added a
      cryptographic token definition.

   o  Added figure titles.

   o  Added server response 401 when client tried to authenticate using
      multiple credentials.

   o  Clarified support for TLS alternatives, and added requirement for
      TLS 1.2 support for token endpoint.

   o  Removed all signature and cryptography.

   o  Removed all discovery.

   o  Updated HTML4 reference.

   -05

   o  Corrected device example.

   o  Added client credentials parameters to the assertion flow as
      OPTIONAL.

   o  Added the ability to send client credentials using an HTTP
      authentication scheme.

   o  Initial text for the "WWW-Authenticate" header (also added scope
      support).

   o  Change authorization endpoint to end-user endpoint.

   o  In the device flow, change the "user_uri" parameter to
      "verification_uri" to avoid confusion with the end-user endpoint.





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   o  Add "format" request parameter and support for XML and form-
      encoded responses.

   -04

   o  Changed all token endpoints to use "POST"

   o  Clarified the authorization server's ability to issue a new
      refresh token when refreshing a token.

   o  Changed the flow categories to clarify the autonomous group.

   o  Changed client credentials language not to always be server-
      issued.

   o  Added a "scope" response parameter.

   o  Fixed typos.

   o  Fixed broken document structure.

   -03

   o  Fixed typo in JSON error examples.

   o  Fixed general typos.

   o  Moved all flows sections up one level.

   -02

   o  Removed restriction on "redirect_uri" including a query.

   o  Added "scope" parameter.

   o  Initial proposal for a JSON-based token response format.

   -01

   o  Editorial changes based on feedback from Brian Eaton, Bill Keenan,
      and Chuck Mortimore.

   o  Changed device flow "type" parameter values and switch to use only
      the token endpoint.

   -00





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   o  Initial draft based on a combination of WRAP and OAuth 1.0a.


9.  References

9.1.  Normative References

   [I-D.ietf-httpbis-p1-messaging]
              Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
              Masinter, L., Leach, P., Berners-Lee, T., and J. Reschke,
              "HTTP/1.1, part 1: URIs, Connections, and Message
              Parsing", draft-ietf-httpbis-p1-messaging-09 (work in
              progress), March 2010.

   [NIST FIPS-180-3]
              National Institute of Standards and Technology, "Secure
              Hash Standard (SHS). FIPS PUB 180-3, October 2008".

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [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.

   [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.

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

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO



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              10646", STD 63, RFC 3629, November 2003.

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

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

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

   [RFC5849]  Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
              April 2010.

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

9.2.  Informative References

   [I-D.hammer-oauth]
              Hammer-Lahav, E., "The OAuth 1.0 Protocol",
              draft-hammer-oauth-10 (work in progress), February 2010.

   [I-D.hardt-oauth]
              Hardt, D., Tom, A., Eaton, B., and Y. Goland, "OAuth Web
              Resource Authorization Profiles", draft-hardt-oauth-01
              (work in progress), January 2010.

   [OASIS.saml-core-2.0-os]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocol for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005.










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Authors' Addresses

   Eran Hammer-Lahav (editor)
   Yahoo!

   Email: eran@hueniverse.com
   URI:   http://hueniverse.com


   David Recordon
   Facebook

   Email: davidrecordon@facebook.com
   URI:   http://www.davidrecordon.com/


   Dick Hardt
   Microsoft

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






























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