Network Working Group                               E. Hammer-Lahav, Ed.
Internet-Draft                                                    Yahoo!
Obsoletes: 5849 (if approved)                                D. Recordon
Intended status: Standards Track                                Facebook
Expires: January 12, June 4, 2011                                           D. Hardt
                                                               Microsoft
                                                           July 11,
                                                        December 1, 2010

                    The OAuth 2.0 Protocol
                         draft-ietf-oauth-v2-10 Framework
                         draft-ietf-oauth-v2-11

Abstract

   This specification describes the OAuth 2.0 protocol. protocol framework.

Status of this Memo

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

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   This Internet-Draft will expire on January 12, June 4, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7
     1.4.  Client Profiles  . . .  Access Grants  . . . . . . . . . . . . . . . . . . 10
       1.4.1.  Web Server . . . .  8
       1.4.1.  Authorization Code . . . . . . . . . . . . . . . . . . 10  8
       1.4.2.  User-Agent . . . . . . . . . . . . .  Resource Owner Password Credentials  . . . . . . . . . 11 10
       1.4.3.  Native Application  Client Credentials . . . . . . . . . . . . . . . . . . 13 10
       1.4.4.  Autonomous  Refresh Token  . . . . . . . . . . . . . . . . . . . . 11
       1.4.5.  Assertion  . . 14
   2.  Client Credentials . . . . . . . . . . . . . . . . . . . . 12
   2.  Client Profiles  . . 14
     2.1.  Client Password Credentials . . . . . . . . . . . . . . . 15
   3.  Obtaining End-User Authorization . . . . . . 12
     2.1.  Web Server . . . . . . . . . 16
     3.1.  Authorization Response . . . . . . . . . . . . . . . 12
     2.2.  User-Agent . . . 18
     3.2.  Error Response . . . . . . . . . . . . . . . . . . . . . 14
     2.3.  Native Application . 20
       3.2.1.  Error Codes . . . . . . . . . . . . . . . . . . . 15
     2.4.  Autonomous . . 21
   4.  Obtaining an Access Token . . . . . . . . . . . . . . . . . . 21
     4.1.  Access Grant Types . . . . 16
   3.  Client Credentials . . . . . . . . . . . . . . . . 23
       4.1.1.  Authorization Code . . . . . . 17
     3.1.  Client Password Credentials  . . . . . . . . . . . . 23
       4.1.2.  Resource Owner Password Credentials . . . 17
     3.2.  Client Assertion Credentials . . . . . . 24
       4.1.3.  Assertion . . . . . . . . . 18
   4.  Obtaining End-User Authorization . . . . . . . . . . . . . 24
       4.1.4.  Refresh Token . . 20
     4.1.  Authorization Request  . . . . . . . . . . . . . . . . . . 25 20
     4.2.  Access Token  Authorization Response . . . . . . . . . . . . . . . . . . 26 22
     4.3.  Error Response . . . . . . . . . . . . . . . . . . . . . . 27 24
       4.3.1.  Error Codes  . . . . . . . . . . . . . . . . . . . . . 28 25
   5.  Accessing a Protected Resource  Obtaining an Access Token  . . . . . . . . . . . . . . . . 29 . . 25
     5.1.  Authenticated Requests  Access Grant Types . . . . . . . . . . . . . . . . . . 29 . . 27
       5.1.1.  The  Authorization Request Header Field Code . . . . . . . . 30
       5.1.2.  URI Query Parameter . . . . . . . . . . 27
       5.1.2.  Resource Owner Password Credentials  . . . . . . . 30 . . 27
       5.1.3.  Form-Encoded Body Parameter  Client Credentials . . . . . . . . . . . . . 31
     5.2.  The WWW-Authenticate Response Header Field . . . . . 28
       5.1.4.  Refresh Token  . . . 32
       5.2.1.  Error Codes . . . . . . . . . . . . . . . . . 28
       5.1.5.  Assertion  . . . . 33
   6.  Extensibility . . . . . . . . . . . . . . . . . . 29
     5.2.  Access Token Response  . . . . . . 34
     6.1.  Defining New Client Credentials Types . . . . . . . . . . 34
     6.2.  Defining New Endpoint Parameters . . 30
     5.3.  Error Response . . . . . . . . . . . 34
     6.3.  Defining New Header Field Parameters . . . . . . . . . . . 35
     6.4.  Defining New Access Grant Types 31
       5.3.1.  Error Codes  . . . . . . . . . . . . . 35
   7.  Security Considerations . . . . . . . . 32
   6.  Accessing a Protected Resource . . . . . . . . . . . 35
   8.  IANA Considerations . . . . . 33
     6.1.  Access Token Types . . . . . . . . . . . . . . . . 35
     8.1.  The OAuth Parameters Registry . . . . 33
     6.2.  The WWW-Authenticate Response Header Field . . . . . . . . 33
       6.2.1.  Error Codes  . . . . . . . . . . . . . . . . . . . . . 35
       8.1.1.
   7.  Extensibility  . . . . . . . . . . . . . . . . . . . . . . . . 36
     7.1.  Defining New Client Credentials Types  . . . . . . . . . . 36
     7.2.  Defining New Endpoint Parameters . . . . . . . . . . . . . 36
     7.3.  Defining New Header Field Parameters . . . . . . . . . . . 36
     7.4.  Defining New Access Grant Types  . . . . . . . . . . . . . 37
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 37
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 37
     9.1.  The OAuth Parameters Registry  . . . . . . . . . . . . . . 37
       9.1.1.  Registration Template  . . . . . . . . . . . . . . . . 36
       8.1.2. 37
       9.1.2.  Example  . . . . . . . . . . . . . . . . . . . . . . . 36 38
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . . 37 38
   Appendix B.  Contributors  . . . . . . . . . . . . . . . . . . . . 37 38
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 37 39
   Appendix D.  Document History  . . . . . . . . . . . . . . . . . . 38
   9. 39
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     9.1. 44
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 42
     9.2. 44
     10.2. Informative References . . . . . . . . . . . . . . . . . . 43 45
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43 46

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 addresses 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 the client obtains an access token (a - a string which
   denotes a specific scope, duration, and other attributes).  The format and
   structure of access attributes.  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
   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

   Access tokens can have different formats, structures, and methods of
   utilization (e.g. cryptographic properties), based on the resource
   server security requirements.  Access token attributes and the
   methods used to access protected resources are beyond the scope of
   this specification and are defined by [RFC2818]).  Other specifications may
   extend it for use with other transport protocols. companion specifications.  The
   interaction between the authorization server and resource server is
   beyond the scope of this specification.

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; 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.

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

   access grant  A general term used to describe the intermediate
         credentials (such as an end-user password or authorization
         code) representing the resource owner authorization.  Access
         grants are used by the client to obtain an access token.  By
         exchanging access grants of different types for an access
         token, the resource server is only required to support a single
         authentication scheme.

   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.  A single authorization server
         may issue tokens for multiple resource servers.

   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. 4.

   token endpoint
         The authorization server's HTTP endpoint capable of issuing
         tokens and refreshing expired tokens.  The token endpoint is
         described in Section 4. 5.

   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
         Section 2. 3.

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 (access grant) 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.

   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)--        |--(A)- Authorization Request --->| ->|   Resource    |
     |        |                               |     Owner     |
     |        |<-(B)------        |<-(B)----- Access Grant ---------| -------|               |
     |        |                               +---------------+
     |        |
     |        |         Client Credentials           Access Grant &      +---------------+
     |        |--(C)------ Access Grant -------->|        |--(C)--- Client Credentials -->| Authorization |
     | Client |                               |     Server    |
     |        |<-(D)------        |<-(D)----- Access Token ---------| -------|               |
     |        |      (w/ Optional Refresh Token)                               +---------------+
     |        |
     |        |                               +---------------+
     |        |--(E)------        |--(E)----- Access Token -------->| ------>|    Resource   |
     |        |                               |     Server    |
     |        |<-(F)----        |<-(F)--- Protected Resource -----| ---|               |
     +--------+                               +---------------+
                     Figure 1: Abstract Protocol Flow

   The abstract flow illustrated in Figure 1 describes the overall
   protocol architecture and includes the following steps:

   (A)  The client requests authorization from the resource owner.  The
        client should not
        authorization request can be made directly to the resource owner's credentials
        directly.  Instead, it should request authorization
        owner, or preferably indirectly via an intermediary such as an
        authorization server or other entities.  For example, the server.

   (B)  The client
        directs receives an access grant which represents the
        authorization provided by the resource owner to owner.

   (C)  The client requests an access token by authenticating with the
        authorization server which in
        turn issues it an using its client credentials, and
        presenting the access grant.  When unavoidable,

   (D)  The authorization server validates the client
        interacts directly with the end-user, asking for the end-user's
        username credentials and password.  If
        the access grant, and if valid issues an access token.

   (E)  The client is acting autonomously,
        the authorization makes a protected resource request is beyond to the scope of this
        specification.

   (B) resource
        server by presenting the access token.

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

1.4.  Access Grants

   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 type depends on the method used by
   the client and supported by the authorization server.  Section 3 describes how server to obtain an it.

1.4.1.  Authorization Code

   The 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 by directing the client to utilize existing
           trust relationships
   end-user to obtain an access token.  They provide
           a bridge between OAuth and other trust frameworks. authorization server.  The
           access grant represented by an assertion depends on authorization server
   authenticates the
           assertion type, its content, end-user, obtains authorization, and how it was issued, which are
           beyond issues the scope of this specification.

        *  Resource owner password credentials - obtained when
           interacting directly an
   authorization code to the client.  Because the end-user only
   authenticates with a resource-owner.  Resource owner the authorization server, the end-user's password credentials (i.e. a username and password) should
           only be used when there
   is a high degree of trust between never shared with the
           resource owner and client.

   The authorization code access grant is suitable when the client (e.g. its computer operating
           system or is
   interacting with an end-user via a highly privileged application).  However, unlike
           the HTTP Basic authentication scheme defined user-agent.

     +----------+
     |          |
     | End-User |
     |          |
     +----------+
          ^
          |
         (B)
     +----|-----+        Client Identifier     +---------------+
     |         -+--(A)--- & Redirect URI ----->|               |
     |  User-   |                              | Authorization |
     |  Agent  -|--(B)-- User authenticates -->|     Server    |
     |          |                              |               |
     |         -+--(C)-- Authorization Code --<|               |
     +-|----|---+                              +---------------+
      (A)  (C)
       |    |
       ^    v
     +---------+
     |         |
     |  Client |
     |         |
     +---------+

                 Figure 2: Obtaining an Authorization Code

   The authorization code flow illustrated in [RFC2617], Figure 2 includes the resource owner's credentials are used for a single
           request and are exchanged for an access token and refresh
           token.  This eliminates
   following steps:

   (A)  The client initiates the need for flow by directing the client end-user's user-
        agent to store the
           resource-owner's credentials for future use.

   (C) authorization server's end-user authorization
        endpoint.  The client requests an access token by authenticating with includes its client identifier, requested
        scope, local state, and a redirection URI (to which the
        authorization server, and presenting server will send the user-agent back once access grant.  The
        token request
        is described in Section 4.

   (D) granted or denied).

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

   (C)  If access token with an optional
        refresh token.  Access tokens usually have a shorter lifetime
        than is granted, the access grant.  Refresh tokens usually have a lifetime
        equal authorization server directs the user-
        agent back to the duration of client using the access grant.  When redirection URI provided.
        The authorization server includes an access token
        expires, authorization code for the refresh token is used
        client to obtain a new access token
        without having use to request another obtain an access grant from token.

   Once the resource
        owner.

   (E)  The client makes a protected resource request to obtains an authorization code, it requests an access
   token by authenticating with the resource
        server, authorization server (using its
   client credentials) and presents presenting the authorization code (access
   grant).

   In cases where the client is incapable of maintaining its client
   credentials secret (such as native applications or an application
   implemented as a user-agent script), the authorization server issues
   an access token in order directly to gain access.
        Accessing a protected resource the client in step (C), instead of
   issuing an authorization code.

   Obtaining an authorization code is described in Section 5.

   (F) 4.

1.4.2.  Resource Owner Password Credentials

   The resource server validates the access token, owner password credentials (e.g. a username and if valid,
        serves
   password) can be used directly as an access grant to obtain an access
   token.  The credentials should only be used when there is a high
   degree of trust between the request.

   When resource owner and the client is acting on (e.g. its own behalf (the
   computer operating system or a highly privileged application), and
   when other access grant types are not available (such as an
   authorization code).

   Even though this grant type requires direct client is also access to the
   resource owner), owner's credentials, the client does not obtain resource owner's credentials are
   used for a single request and are exchanged for an access grant.  The
   simplified protocol flow is illustrated token.
   Unlike the HTTP Basic authentication scheme defined in [RFC2617],
   this grant type eliminates the need for the client to store the
   resource-owner's credentials for future use.

   In Figure 2:

     +--------+                                  +---------------+
     |        |--(C)--- Client Credentials ----->| Authorization |
     |        |                                  |     Server    |
     |        |<-(D)------ Access Token ---------|               |
     |        |                                  +---------------+
     | Client |
     |        |                                  +---------------+ 3, the client requests authorization from the resource
   owner directly.  When the resource owner is an end-user, the client
   typically prompts the end-user for the username and password.

     +--------+                               +----------+
     |        |--(E)------ Access Token -------->|        |--(A)- Authorization Request ->| Resource |
     | Client |                               |     Server   Owner  |
     |        |<-(F)---- Protected Resource -----|        |<-(B)-- Username & Password ---|          |
     +--------+                                  +---------------+                               +----------+

          Figure 2: Protocol Flow for 3: Obtaining Resource Owner Password Credentials

1.4.3.  Client Acting On Its Own Behalf

   When the Credentials

   The client uses credentials can be used as an access grant when the user-agent profile (described in
   Section 1.4.2),
   authorization scope is limited to the protected resources under the
   control of the client, or other protected resources previously
   arranged with the authorization request results in server.  Client credentials are used
   as an access grant typically when the client is acting on its own
   behalf (the client is also the resource owner).

1.4.4.  Refresh Token

   Access tokens usually have a shorter lifetime than authorized by the
   resource owner.  When issuing an access token, the authorization
   server can include a refresh token which is used by the client to
   obtain a new access token when the current access token expires.
   When requesting a new access token, the refresh token acts as illustrated in Figure 3: an
   access grant.  Using a refresh token removes the need to interact
   with the resource owner again, or to store the original access grant
   used to obtain the access token and refresh token.

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

               Figure 3: Indirect Access Grant Protocol Flow

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 ---|    Resource   |
     | Authorization Client |                              |    at    |<---(B)-- User authenticates --->|     Server    |
     | Browser  |                                 |               |
     |         -+----(C)-- Authorization Code ---<|        |--(E)----- Access Token ----->|               |
     +-|----|---+                                 +---------------+
     |        |                                         ^      v
      (A)  (C)                              |               |
     |        |<-(F)-- Invalid Token Error --|               |
     |        |
       ^    v                              +---------------+
     |        |
     +---------+
     |        |          Refresh Token &     +---------------+
     |         |>---(D)--        |--(G)-- Client Credentials, --------'      |
     |   Web   | Credentials -->| Authorization Code,                | |  Client |            & Redirect URI
     |        |                              |     Server    |
     |         |<---(E)-----        |<-(H)----- Access Token -------------------'
     +---------+       (w/ ------|               |
     +--------+     & Optional Refresh Token) Token +---------------+

                   Figure 4: Web Server Flow Refreshing an Access Token

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

   (A)  The web client initiates the flow requests an access token by redirecting the end-user's
        user-agent to authenticating with the end-user
        authorization endpoint as described
        in Section 3.  The client includes server using its client identifier,
        requested scope, local state, credentials, and a redirect URI to which the
        authorization server will send the end-user back once
        presenting an access is
        granted (or denied). grant.

   (B)  The authorization server authenticates the end-user (via validates the
        user-agent) client credentials 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 grant, and if valid issues an access token and a
        refresh token.

   (D)

   (C)  The client makes a protected resource requests an access token from to the authorization resource
        server by authenticating and including the authorization code
        received in presenting the previous step as described in Section 4.

   (E) access token.

   (D)  The authorization resource server validates the client credentials access token, and if valid,
        serves the authorization code request.

   (E)  Steps (C) and responds back with (D) repeat until 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 token expires.  If the
        client is based on
   the user-agent's same-origin policy.

   Unlike other profiles in which does not know the client makes separate requests for
   end-user authorization and access token, the client receives token expired, it makes another
        protected resource request.  Otherwise, it skips to step (G).

   (F)  Since the access token as a result of the end-user authorization request in is invalid (expired), the
   form of resource server
        returns an HTTP redirection. invalid token error.

   (G)  The client requests a new access token by authenticating with
        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 using its client credentials, and
        presenting the access refresh token from the response and passing it to (as the client.

   This user-agent profile does not utilize access grant).

   (H)  The authorization server validates the client secret since credentials and
        the
   client executables reside refresh token, and if valid issues a new access token (and
        optionally, a new refresh token).

1.4.5.  Assertion

   Assertions provide a bridge between OAuth and other trust frameworks.
   They enable the client to utilize existing trust relationships in
   order to obtain an access token.  The access grant represented by an
   assertion depends on the end-user's computer or device assertion type, its content, and how it was
   issued, which
   makes are beyond the client secret accessible and exploitable.  Because scope of this specification.

   Assertions are used as part of the protocol extensibility model,
   providing a way for authorization servers to support additional
   access token is encoded into grant types.

2.  Client Profiles

   [[ add intro and find new names for the redirection URI, it may be exposed profiles. this section will
   have normative language in future drafts, similar to -05 and earlier.
   ]]

2.1.  Web Server

   The web server profile is suitable for clients capable of interacting
   with the end-user end-user's user-agent (typically a web browser) and other applications residing on capable
   of receiving incoming requests (via redirection) from the computer or
   device.
   authorization server (capable of acting as an HTTP server).

     +----------+          Client Identifier     +----------------+      +---------------+
     |          |>---(A)--         -+----(A)--- & Redirection Redirect URI --->| ------>|               |
     | End-user |                                 | Authorization |
   End <--+  -  -  - +----(B)--
     |    at    |<---(B)-- User authenticates -->|  Authorization --->|     Server    |
   User
     | Browser  |                                 |     Server               |
     |          |<---(C)--- Redirect URI -------<|         -+----(C)-- Authorization Code ---<|               |
     +-|----|---+                                 +---------------+
       |  Client    |         with Access Token                                         ^      v
      (A)  (C)                                        |      |
       |    in    |            in Fragment         +----------------+                                         |  Browser      |
       ^    v                                         |      |                                +----------------+
     +---------+                                      |          |>---(D)--- Redirect URI ------->|      |
     |         |>---(D)-- Client Credentials, --------'      |         without Fragment
     |   Web  Server |          Authorization Code,                |
     |  -Based |   with Client  |
          |    (F)   |<---(E)--- Web Page with ------<|    Resource    |            & Redirect URI                   |  Access
     |              Script  Client |                                             |
     |   Token  |                                +----------------+
          +----------+         |<---(E)----- Access Token -------------------'
     +---------+       (w/ Optional Refresh Token)

                         Figure 5: User-Agent Web Server Flow

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

   (A)  The web client sends initiates the flow by redirecting the end-user's
        user-agent to the end-user authorization endpoint as described
        in Section 3. 4.  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 access 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  Assuming the end-user granted access, the authorization server
        redirects the user-agent back to the client to the redirection
        URI provided earlier.  The redirection URI authorization includes an
        authorization code for the client to use to obtain an access token in the
        URI fragment.
        token.

   (D)  The user-agent follows the redirection instructions by making a
        request to client requests an access token from the web authorization
        server which does not include by authenticating and including the fragment.
        The user-agent retains authorization code
        received in the fragment information locally. previous step as described in Section 5.

   (E)  The web authorization server returns a web page (typically an HTML page validates the client credentials and
        the authorization code and responds back with
        an embedded script) capable the access token.

2.2.  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 accessing the full redirection
        URI including client is based on
   the fragment retained by user-agent's same-origin policy.

   Unlike other profiles in which the user-agent, client makes separate requests for
   end-user authorization and
        extracting access token, the client receives the
   access token (and other parameters) contained as a result of the end-user authorization request in the fragment.

   (F)
   form of an HTTP redirection.  The user-agent executes client requests the script provided by authorization
   server to redirect the user-agent to another web server
        locally, or local
   resource accessible to the user-agent which extracts is capable of extracting
   the access token from the response and passes passing it to the client.

1.4.3.  Native Application

   Native application are clients running as native code

   This user-agent profile does not utilize the client secret since the
   client executables reside on the end-
   user's 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) 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's user-agent but are limited in how
   such interaction affects their end-user experience.  In many cases,
   native and other applications are incapable of receiving direct callback
   requests from residing on the server (e.g. firewall, operating system
   restrictions).

   Native application clients can be implemented computer or
   device.

          +----------+          Client Identifier     +----------------+
          |          |>---(A)-- & Redirection URI --->|                |
          |          |                                |                |
   End <--+  -  -  - +----(B)-- User authenticates -->|  Authorization |
   User   |          |                                |     Server     |
          |          |<---(C)--- Redirect URI -------<|                |
          |  Client  |         with Access Token      |                |
          |    in different ways based
   on their requirements and desired end-user experience.  Native
   application clients can:

   o  Utilize    |            in Fragment         +----------------+
          |  Browser |
          |          |                                +----------------+
          |          |>---(D)--- Redirect URI ------->|                |
          |          |         without Fragment       |   Web Server   |
          |          |                                |   with Client  |
          |    (F)   |<---(E)--- Web Page with ------<|    Resource    |
          |  Access  |              Script            |                |
          |   Token  |                                +----------------+
          +----------+
                         Figure 6: User-Agent Flow

   The user-agent flow illustrated in Figure 6 includes the following
   steps:

   (A)  The client sends the user-agent to the end-user authorization
        endpoint as described in Section 3 by launching an external user-agent. 4.  The client can
      capture the response by providing a redirection URI with a custom
      URI scheme (registered with the operating system to invoke the includes its
        client application), or by providing identifier, requested scope, local state, and a redirection redirect
        URI pointing to
      a server-hosted resource under the client's control which makes the response available to authorization server will send the client (e.g. using end-user
        back once authorization is granted (or denied).

   (B)  The authorization server authenticates the window title end-user (via the
        user-agent) and establishes whether the end-user grants or other locations accessible from outside
        denies the user-agent).

   o  Utilize client's access request.

   (C)  If the end-user authorization endpoint as described in
      Section 3 by using an embedded user-agent.  The client obtains granted access, the
      response by directly communicating with authorization server
        redirects the embedded user-agent.

   o  Prompt end-users for their password and use them directly user-agent to
      obtain an the redirection URI provided
        earlier.  The redirection URI includes the access token.  This is generally discouraged, as it
      hands token in the end-user's password directly
        URI fragment.

   (D)  The user-agent follows the redirection instructions by making a
        request to the third-party client web server which in turn has to store it in clear-text.  It also requires does not include the fragment.
        The user-agent retains the fragment information locally.

   (E)  The web server to support password-based authentication.

   When choosing between launching returns a web page (typically an external browser and HTML page with
        an embedded
   user-agent, developers should consider script) capable of accessing the following:

   o  External user-agents may improve completion rate as full redirection
        URI including the end-user
      may already be logged-in fragment retained by the user-agent, and not have to re-authenticate.

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

   o  Embedded user-agents pose a security challenge because users are
      authenticating access token (and other parameters) contained in an unidentified window without
        the fragment.

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

1.4.4.  Autonomous

   Autonomous
        client.

2.3.  Native Application

   Native applications are clients utilize an existing trust relationship running as native code on the end-
   user's computer or
   framework to establish authorization.  Autonomous 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 the
   existing trust framework they rely upon.  Autonomous desired end-user experience.  Native
   application clients can:

   o  Obtain an access token by authenticating with  Utilize the end-user authorization
      server using their client credentials. endpoint as described in
      Section 4 by launching an external user-agent.  The scope of client can
      capture the access
      token is limited response by providing a redirection URI with a custom
      URI scheme (registered with the operating system to invoke the protected resources
      client application), or by providing a redirection URI pointing to
      a server-hosted resource under the client's control of which makes
      the client, or that of another resource owner previously arranged
      with response available to the authorization server.

   o  Use an existing access grant expressed as an assertion client (e.g. using an
      assertion format supported by the authorization server.  Using
      assertions requires window title
      or other locations accessible from outside the user-agent).

   o  Utilize the end-user authorization endpoint as described in
      Section 4 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 a assertion (such as a
      SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
      or access token.  This is generally discouraged, as it
      hands the end-user's password directly to self-issue an assertion.  The assertion format, the process
      by third-party client
      which in turn has to store it in clear-text.  It also requires the assertion is obtained,
      server to support password-based authentication.

   When choosing between launching an external browser and an embedded
   user-agent, developers should consider the method of validating
      the assertion are defined by following:

   o  External user-agents may improve completion rate as the assertion issuer 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
      authorization server, need to switch context and open new windows.

   o  Embedded user-agents pose a security challenge because users are beyond
      authenticating in an unidentified window without access to the scope of this
      specification.

2.  Client Credentials

   When interacting
      visual protections offered by many user-agents.

2.4.  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, the client identifies
   itself
      server using a their client identifier and authenticates using a set 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 credentials.  This specification provides one mechanism for
   authenticating to obtain an 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.

3.  Client Credentials

   When interacting with the authorization server, the client identifies
   itself using password credentials. a set of client credentials which include a client
   identifier and other properties for client authentication.  The means
   through which the client obtains its credentials are beyond the scope
   of this specification, but usually typically 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. client.  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. schemes.  The
   client MUST NOT utilize include more than one set of credentials or
   authentication mechanism with each request.

2.1.

3.1.  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&

     grant_type=authorization_code&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: parameters:

   client_id
         REQUIRED.  The client identifier.

   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.

3.  Obtaining End-User Authorization

   When the password credentials.

3.2.  Client Assertion Credentials

   The client interacts with an end-user, the end-user MUST first
   grant the assertion credentials are used in cases where a password
   (clear-text shared symmetric secret) is unsuitable or does not
   provide sufficient security for client authorization to access its protected resources.
   Once obtained, the end-user access grant authentication.  In such cases
   it is expressed common to use other mechanisms such as an
   authorization code which the HMAC or digital
   signatures that do not require sending clear-text secrets.  The
   client uses assertion credentials provide an extensible mechanism to obtain use
   an access token.
   To obtain an end-user authorization, the client sends the end-user to
   the end-user authorization endpoint.

   At assertion format supported by the end-user authorization endpoint, server for
   authentication the end-user first
   authenticates with client.

   Using assertions requires the authorization server, and then grants client to obtain an assertion (such as
   a SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
   or
   denies the access request. to self-issue an assertion.  The way in which assertion format, the authorization server
   authenticates process by
   which the end-user (e.g. username assertion is obtained, and password login, OpenID,
   session cookies) the method of validating the
   assertion are defined by the assertion issuer and in which the authorization server obtains the
   end-user's authorization, including whether it uses a secure channel
   such as TLS, is
   server, and are beyond the scope of this specification.  However, the
   authorization server MUST first verify

   When using a client assertion, the identity of client includes the end-user. following
   parameters:

   client_assertion_type  REQUIRED.  The location format of the end-user assertion as
         defined by the authorization endpoint can server.  The value MUST be found in an
         absolute URI.

   client_assertion  REQUIRED.  The client assertion.

   For example, the service documentation, or can be obtained by client sends the following access token request
   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 SAML 2.0 assertion to the end-user authenticate itself (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&code=i1WsRn1uB1&
     client_assertion=PHNhbWxwOl[...omitted for brevity...]ZT4%3D&
     client_assertion_type=
     urn%3Aoasis%3Anames%sAtc%3ASAML%3A2.0%3Aassertion&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

   When obtaining an access token using a client assertion together with
   an authorization endpoint result code (as described in user
   authentication and Section 5.1.1), a mechanism is
   needed to map between the transmission value of sensitive information, "client_id" parameter used to
   obtain the authorization server SHOULD require code, and the use of a transport-layer
   security client assertion.  Such
   mechanism such as TLS when sending requests to is beyond the end-user out of scope for this specification, but MUST
   be specified for any client assertion type used in combination with
   an authorization endpoint.

   In order to direct the end-user's user-agent to the code.

   The authorization
   server, the server MUST reject access token requests using
   client constructs the request URI by adding assertion credentials that do not contain HMAC or signed
   values that:

   o  State the following
   parameters assertion was specifically issued to be consumed by the end-user authorization
      receiving 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, (typically via an
         authorization code, audience or both.  The parameter recipient value MUST be set
         to "token" for requesting
      containing the receiving endpoint's identifier).

   o  Identify the entity that issued the assertion (typically via an access token, "code" for
         requesting
      issuer value).

   o  Identify when the assertion expires as an authorization code, or "code_and_token" to
         request both. absolute time (typically
      via an expiration value containing a UTC date/time value).  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 MUST reject expired assertions.

4.  Obtaining End-User Authorization

   Before the
         specification ]]

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

   redirect_uri
         REQUIRED, unless can access a redirection URI has been established between
         the client and protect resource, it MUST first obtain
   authorization server via other means.  An
         absolute URI to which from the authorization server will redirect end-user.  To obtain an end-user
   authorization, the user-agent client sends the end-user to when the end-user
   authorization step endpoint.  Once obtained, the end-user access grant is
         completed.  The
   expressed as an authorization server SHOULD require code which the client uses to pre-register their redirection URI.

   scope
         OPTIONAL.  The scope of the obtain an
   access request expressed as a list
         of space-delimited strings.  The value of the "scope" parameter
         is defined by token.

   At the end-user authorization server.  If endpoint, the value contains
         multiple space-delimited strings, their order does not matter, end-user first
   authenticates with the authorization server, and each string adds an additional access range to then grants or
   denies the
         requested scope.

   state
         OPTIONAL.  An opaque value used by access request.  The way in which the client to maintain state
         between authorization server
   authenticates the request end-user (e.g. username and callback.  The password login, OpenID,
   session cookies) and in which the authorization server
         includes obtains the
   end-user's authorization, including whether it uses a secure channel
   such as TLS, is beyond the scope of this value when redirecting specification.  However, the user-agent back to
   authorization server MUST first verify the
         client. identity of the end-user.

   The client directs location of the end-user to authorization endpoint can be found in
   the constructed service documentation.  The end-user authorization endpoint URI using an HTTP
   redirection response, or
   MAY include a query component as defined by other means available [RFC3986] section 3,
   which must be retained when adding additional query parameters.

   Since requests to it via the end-
   user's user-agent.  The end-user authorization server MUST support endpoint result in user
   authentication and the use transmission of sensitive information, the HTTP "GET" method for the end-user
   authorization endpoint, and
   MAY support server SHOULD require the use of the "POST" method a transport-layer
   security mechanism such as well.

   For example, the client directs the end-user's user-agent TLS when sending requests 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 end-user
   authorization endpoint.

4.1.  Authorization Request

   In order to direct the client has previously registered a redirection URI with end-user's user-agent to the authorization
   server, the authorization server MUST verify that client constructs the
   redirection request URI received matches by adding the registered following
   parameters to the end-user authorization endpoint URI associated with query component
   using the client identifier. [[ provide guidance on how to perform matching
   ]]

   Parameters sent without a value MUST be treated "application/x-www-form-urlencoded" format as if they were
   omitted from the request. defined by
   [W3C.REC-html401-19991224]:

   response_type
         REQUIRED.  The requested response: an access token, an
         authorization server SHOULD ignore
   unrecognized request parameters. code, or both.  The parameter value MUST be set
         to "token" for requesting an access token, "code" for
         requesting an authorization server validates the request code, or "code_and_token" to ensure all required
   parameters are present and valid.  If the
         request is invalid, the both.  The authorization server immediately redirects the user-agent back MAY decline to the provide
         one or more of these response types.

   client_id
         REQUIRED.  The client using the redirection URI provided with the appropriate error
   code identifier as described in Section 3.2.

   The authorization server authenticates 3.

   redirect_uri
         REQUIRED, unless a redirection URI has been established between
         the end-user client and obtains an authorization decision (by asking the end-user or by establishing
   approval server via other means).  When a decision has been established, means.  An
         absolute URI to which the authorization server directs will redirect
         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 when 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 step is issued.
         completed.  The authorization server MUST invalidate the authorization code after a single
         usage.  The authorization code is bound to SHOULD require the client
         identifier and
         to pre-register their 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 request expressed as a list
         of space-
         delimited strings if an access token is included. 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.

   state
         REQUIRED if the "state" parameter was present in
         OPTIONAL.  An opaque value used by the client
         authorization request.  Set to maintain state
         between the exact request and callback.  The authorization server
         includes this value received from when redirecting the user-agent back to the
         client.

   The method in which the authorization server adds client directs the parameter end-user to the redirection constructed URI is determined using an HTTP
   redirection response, or by other means available to it via the response type requested by
   the client in the end-
   user's user-agent.  The authorization request using server MUST support the "response_type"
   parameter.

   If use of
   the response type is "code", HTTP "GET" method for the end-user authorization server adds the
   parameters to endpoint, and
   MAY support the redirection URI query component using use of the
   "application/x-www-form-urlencoded" format "POST" method as defined by
   [W3C.REC-html401-19991224]. well.

   For example, the authorization server redirects client directs the end-user's user-
   agent by sending user-agent to make the
   following HTTP response: 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/1.1 302 Found
     Location: https://client.example.com/cb?code=i1WsRn1uB1
     Host: server.example.com

   If the response type is "token", client has previously registered a redirection URI with the
   authorization server adds server, the
   parameters to authorization server MUST verify that the
   redirection URI fragment component using received matches the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224].

   For example, registered URI associated with
   the client identifier.  The authorization server redirects SHOULD NOT redirect
   the end-user's user-
   agent by sending user-agent to unregistered or untrusted URIs to prevent the following HTTP response:

    HTTP/1.1 302 Found
    Location: http://example.com/rd#access_token=FJQbwq9&expires_in=3600
   endpoint from being used as an open redirector.  If the response type no valid
   redirection URI is "code_and_token", available, the authorization server
   adds the "code" and "state" parameters to SHOULD inform
   the redirection URI query
   component and end-user of the "access_token", "scope", and "expires_in" error occured. [[ provide guidance on how to the
   redirection URI fragment using the
   "application/x-www-form-urlencoded" format
   perform matching ]]

   Parameters sent without a value MUST be treated as defined by
   [W3C.REC-html401-19991224].

   For example, if they were
   omitted from the request.  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 request 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 server validates the access request or if to ensure all required
   parameters are present and valid.  If the request is invalid, the
   authorization server informs the client by adding redirects the
   following parameters user-agent back to the client
   using the redirection URI query component using provided with the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224]:

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

   error_description  OPTIONAL.  A human-readable text providing
         additional information, used to assist in 4.3.

   The authorization server authenticates the understanding end-user 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 obtains an
   authorization decision (by asking the end-user
         with additional information about or by establishing
   approval via other means).  When a decision has been established, the error.

   state
         REQUIRED if
   authorization server directs the "state" parameter was present in end-user's user-agent to the
   provided client
         authorization request.  Set redirection URI using an HTTP redirection response,
   or by other means available to it via the exact value received from end-user's user-agent.

4.2.  Authorization Response

   If the client.

   For example, end-user grants the access request, the authorization server redirects
   issues an access token, an authorization code, or both, and delivers
   them to the end-user's user-
   agent client by sending adding the following HTTP response:

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

3.2.1.  Error Codes

   The authorization server includes one of parameters to the following error codes
   with
   redirection URI (as described below):

   code
         REQUIRED if the error response:

   invalid_request
         The request response type is missing a required parameter, includes an
         unsupported parameter or parameter value, "code" or is "code_and_token",
         otherwise
         malformed.

   invalid_client MUST NOT be included.  The client identifier provided is invalid.

   unauthorized_client authorization code
         generated by the authorization server.  The client authorization code
         SHOULD expire shortly after it is not authorized issued to use minimize the requested response
         type.

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

   access_denied risk
         of leaks.  The end-user or client MUST NOT reuse the authorization server denied code.
         If an authorization code is used more than once, the request.

   unsupported_response_type
         authorization server MAY revoke all tokens previously issued
         based on that authorization code.  The requested authorization code is
         bound to the client identifier and redirection URI.

   access_token
         REQUIRED if the response type is not supported "token" or "code_and_token",
         otherwise MUST NOT be included.  The access token issued by the
         authorization server.

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

   [[ Add mechanism for extending error codes ]]

4.  Obtaining

   token_type
         REQUIRED if the response includes an Access Token access token.  The type of
         the token issued.  The token type informs the client obtains an how the
         access token by authenticating with is to be used when accessing a protected resource
         as described in Section 6.1.

   expires_in
         OPTIONAL.  The duration in seconds of the
   authorization server and presenting its access grant (in the form of
   an authorization code, resource owner credentials, token lifetime
         if an assertion, or a
   refresh token).

   Since requests to access token is included.  For example, the value "3600"
         denotes that the access token endpoint result will expire in one hour from the transmission of
   plain text credentials in
         time the HTTP request and response, response was generated by the authorization server MUST require the use server.

   scope
         OPTIONAL.  The scope of a transport-layer
   security mechanism when sending requests to the access token endpoints.
   Servers MUST support TLS 1.2 as defined in [RFC5246], and MAY support
   additional transport-layer security mechanisms.

   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 list of space-
         delimited strings if an 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. included.  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.  The authorization code,
         assertion), server
         SHOULD include the parameter if the requested scope MUST be equal or lesser than is
         different from the scope previously granted.

   In addition, one requested by the client.

   state
         REQUIRED if the "state" parameter was present in the client MUST include
         authorization request.  Set to the appropriate parameters
   listed for exact value received from
         the selected access grant type as described client.

   The method in
   Section 4.1.

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

4.1.  Access Grant Types

   The adds the parameter to
   the redirection URI is determined by the response type requested by
   the client requests an access token using one of in the four types of
   access grants: authorization code, password credentials, assertion,
   or refresh token.

   When requesting an access token request using the "none" access grant "response_type"
   parameter.

   If the response type
   (no access grant is included), "code", the client is requesting access authorization server adds the
   parameters to the
   protected resources under its control, or those of another resource
   owner which has been previously arranged with redirection URI query component using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224].

   For example, the authorization server (the method of which is beyond redirects the scope of this
   specification).

4.1.1.  Authorization Code

   The client includes end-user's user-
   agent by sending the authorization code using following HTTP response:

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

   If the
   "authorization_code" access grant response type and is "token" or "code_and_token", the following parameters:

   code
         REQUIRED.  The
   authorization code received from server adds the parameters to the
         authorization server.

   redirect_uri
         REQUIRED.  The redirection URI used in
   fragment component using the initial request. "application/x-www-form-urlencoded"
   format as defined by [W3C.REC-html401-19991224].

   For example, the client makes authorization server redirects the following HTTP request end-user's user-
   agent by including
   its client credentials via sending the "client_secret" parameter described in
   Section 2 and using transport-layer security (line following HTTP response (URI 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 302 Found
     Location: http://example.com/rd#access_token=FJQbwq9&
               token_type=example&expires_in=3600

   Clients SHOULD ignore unrecognized response parameters.  The authorization server MUST:

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

   o  Verify that other values received from the authorization code and redirection URI server, are all
      valid and match its stored association.

   If the request is valid,
   left undefined by this specification.  Clients should avoid making
   assumptions about value sizes.  Servers should document the authorization server issues a successful
   response as described in Section 4.2.

4.1.2.  Resource Owner Password Credentials

   The client includes expected
   size of any value they issue.

4.3.  Error Response

   If the resource owner credentials using end-user denies the
   "password" access grant type and request or if the following parameters: [[ add
   internationalization consideration request fails for username and password ]]

   username
         REQUIRED.  The resource owner's username.

   password
         REQUIRED.  The resource owner's password.

   For example,
   reasons other than a missing or invalid redirection URI, the
   authorization server informs the client makes by adding the following HTTP request by including
   its client credentials via
   parameters to the "client_secret" parameter described in
   Section 2 and redirection URI query component 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
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224]:

   error
         REQUIRED.  A single error code as described in Section 4.2.

4.1.3.  Assertion

   The client includes the assertion using 4.3.1.

   error_description  OPTIONAL.  A human-readable text providing
         additional information, used to assist in the "assertion" access grant
   type understanding and the following parameters:

   assertion_type
         REQUIRED.  The format
         resolution of the assertion as defined by 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 server.  The request.  Set to the exact value MUST be an absolute URI.

   assertion
         REQUIRED.  The assertion. received from
         the client.

   For example, the client makes 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

   If the request using
   transport-layer security, and client authentication is achieved via fails due to a missing or invalid redirection URI, 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 SHOULD inform the client credentials (if
   present) and end-user of the assertion error, and if valid issues an access token
   response as described in Section 4.2.  The authorization server
   SHOULD
   MUST NOT issue a refresh token (instead, require redirect the client end-user's user-agent to use the same or new assertion).

   Authorization servers SHOULD issue access tokens invalid
   redirection URI.

4.3.1.  Error Codes

   The authorization server includes one of the following error codes
   with a limited
   lifetime and require clients to refresh them by requesting a new
   access token using the same assertion if it error response:

   invalid_request
         The request is still valid.
   Otherwise the client MUST obtain missing a new valid assertion.

4.1.4.  Refresh Token required parameter, includes an
         unsupported parameter or parameter value, or is otherwise
         malformed.

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

   refresh_token
         REQUIRED. identifier provided is invalid.

   unauthorized_client
         The refresh token associated with the access token
         to be refreshed.

   For example, the client makes is not authorized to use 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 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 MUST verify the client credentials (if
   present), the validity of the refresh token, and that the resource
   owner's authorization is still valid.  If denied the request request.

   unsupported_response_type
         The requested response type is valid, not supported by the
         authorization server issues an access token response as described in
   Section 4.2. server.

   invalid_scope
         The authorization server MAY issue a new refresh token.

4.2. requested scope is invalid, unknown, or malformed.

   [[ Add mechanism for extending error codes ]]

5.  Obtaining an Access Token Response

   After receiving and verifying a valid and authorized

   The client obtains an access token
   request from the client, by authenticating with the
   authorization server issues the access
   token and optional refresh token, and constructs the response by
   adding presenting its access grant (in the following parameters form of
   an authorization code, resource owner credentials, an assertion, or a
   refresh token).

   Since requests to the entity body token endpoint result in the transmission of
   clear-text credentials in the HTTP
   response with request and response, the
   authorization server MUST require the use of a 200 (OK) status code:

   The token response contains transport-layer
   security mechanism when sending requests to the following parameters:

   access_token
         REQUIRED. token endpoints.
   Servers MUST support TLS 1.2 as defined in [RFC5246], and MAY support
   additional transport-layer security mechanisms.

   The client requests an access token issued by making an HTTP "POST" request
   to the authorization server.
         The access token string MUST comply with the access-token rule
         defined in Section 5.1.1.

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

   refresh_token
         OPTIONAL. service documentation.  The refresh token used endpoint URI MAY
   include a query component.

   The client authenticates with the authorization server by adding its
   client credentials to obtain new access tokens
         using the same end-user access grant request as described in Section 4.1.4. 3.  The
   authorization server SHOULD NOT issue a
         refresh 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 is set to "none". included in the request.
         Value MUST be one of "authorization_code", "password",
         "refresh_token", "client_credentials", or an absolute URI
         identifying an assertion format supported by the authorization
         server.

   scope
         OPTIONAL.  The scope of the access token request expressed as a list
         of space-
         delimited 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  If the
         parameter if access grant being used already
         represents an approved scope (e.g. authorization code,
         assertion), the requested scope is different from MUST be equal or lesser than
         the one
         requested by scope previously granted, and if omitted is treated as
         equal to the client.

   The parameters are including in previously approved scope.

   In addition, the entity body of client MUST include the HTTP response
   using appropriate parameters
   listed for the "application/json" media selected access grant type as defined by [RFC4627].  The
   parameters are serialized into described in
   Section 5.1.

   Parameters sent without 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 value MUST be treated as JSON numbers. if they were
   omitted from the request.  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 request parameters.

5.1.  Access Grant Types

   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 client requests an access token request is invalid using an authorization code,
   resource owner password credentials, client credentials, refresh
   token, or unauthorized, assertion.

5.1.1.  Authorization Code

   The client includes the authorization
   server constructs code using the response by adding
   "authorization_code" access grant type and the following parameter to
   the entity body of the HTTP response using the "application/json"
   media type:

   error parameters:

   code
         REQUIRED.  A single error  The authorization 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 received from the error occurred.

   error_uri  OPTIONAL.  A
         authorization server.

   redirect_uri
         REQUIRED.  The redirection URI identifying a human-readable web page
         with information about the error, used to provide the end-user
         with additional information about in the error. initial request.

   For example:

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

     {
       "error":"invalid_request"
     }

   If example, the client provided invalid credentials using an HTTP
   authentication scheme via makes the "Authorization" following HTTP request header field, by including
   its client credentials via the "client_secret" parameter described in
   Section 3 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 respond with MUST:

   o  Validate the HTTP 401
   (Unauthorized) status code.  Otherwise, client credentials (if present) and ensure they match
      the authorization server
   SHALL respond with the HTTP 400 (Bad Request) status code.

4.3.1.  Error Codes

   The authorization server includes one of

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

   If 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 valid, the client, or is otherwise malformed.

   invalid_client authorization server issues a successful
   response as described in Section 5.2.

5.1.2.  Resource Owner Password Credentials

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

   unauthorized_client
         The authenticated client is not authorized to use using the
   "password" 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).

   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. following parameters: [[ Add mechanism add
   internationalization consideration for extending error codes username and password ]]

5.  Accessing a Protected Resource

   Clients access protected resources by presenting an access token to
   the

   username
         REQUIRED.  The resource server.  Access tokens act as bearer tokens, where owner's username.

   password
         REQUIRED.  The resource owner's password.

   For example, the
   token string acts as a shared symmetric secret.  This requires
   treating client makes the access token with following HTTP request by including
   its client credentials via the same care as other secrets (e.g.
   end-user passwords).  Access tokens SHOULD NOT be sent "client_secret" parameter described in
   Section 3 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 clear
   over client credentials (if
   present) and end-user credentials and if valid issue an insecure channel.

   However, when it is necessary to transmit access tokens token
   response as described in the clear
   without a secure channel, authorization servers SHOULD issue Section 5.2.

5.1.3.  Client Credentials

   The client can request an access
   tokens with limited scope and lifetime to reduce token using only its client
   credentials using the potential risk
   from a compromised "client_credentials" access token.

   Clients MUST NOT make authenticated requests with grant type.  When
   omitting an explicit access grant, the client is requesting access token to
   unfamiliar resource servers, regardless of
   the presence protected resources under its control, or those of a secure
   channel.

   The another
   resource server MUST validate the access token and ensure it owner which has
   not expired and that its scope covers the requested resource.  The
   methods used by been previously arranged with the resource
   authorization server to validate the access token are (the method of which is 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
   specification).

5.1.4.  Refresh Token

   The client includes the "Authorization"
   request header field.  Resource servers MUST accept authenticated
   requests refresh token using the "OAuth" HTTP authentication scheme as described in
   Section 5.1.1, "refresh_token"
   access grant type and MAY support additional methods.

   Alternatively, clients MAY attempt to include the following parameter:

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

   For example, the client makes the following HTTP request URI in by including
   its client credentials via the query component as "client_secret" parameter described in
   Section 5.1.2, or in the HTTP body when 3 and using the
   "application/x-www-form-urlencoded" content type as described in
   Section 5.1.3.  Resource 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

   The authorization server MAY support these alternative
   methods.

   Clients SHOULD only use MUST verify the request URI or body when client credentials (if
   present), the
   "Authorization" request header field is not available, validity of the refresh token, and MUST NOT
   use more than one method in each request.

5.1.1.  The Authorization Request Header Field

   The "Authorization" that the resource
   owner's authorization is still valid.  If the request header field is used by clients to make
   authenticated valid, the
   authorization server issues an access token requests. response as described in
   Section 5.2.  The client uses authorization server MAY issue a new refresh token,
   in which case, the "OAuth"
   authentication scheme to include client MUST discard the access old refresh token in and
   replace it with the request.

   For example:

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

5.1.5.  Assertion

   The "Authorization" header field uses client includes an assertion by specifying the framework assertion format
   using an absolute URI (as defined by
   [RFC2617] as follows: the authorization server) as the
   value of the "grant_type" parameter and by adding the following
   parameter:

   assertion
         REQUIRED.  The assertion.

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

   The authorization server MUST validate the client credentials    = "OAuth" RWS access-token [ CS 1#auth-param ]
     access-token   = 1*( quoted-char / <"> )

     CS             = OWS "," OWS

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

      NOTE: [RFC5849] defines (if
   present) and the assertion and if valid issues an access token
   response as described in Section 5.2.  The authorization server
   SHOULD NOT issue a different format for refresh token (instead, it should require the "OAuth"
      authentication scheme.  Resource
   client to use the same or new assertion).

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

5.2.  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.

   token_type
         REQUIRED.  The type of the token issued.  The token type
         informs the client how the access token is to be used when
         accessing a protected resource as described in Section 6.1.

   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 5.1.4.  The authorization server SHOULD NOT issue a
         refresh token when the access grant type is an assertion or a
         set of client credentials.

   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
   as JSON numbers.

   The authorization server MUST include the presence HTTP "Cache-Control"
   response header field with a value of the
      "oauth_signature_method" which is REQUIRED "no-store" in the previous version 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",
       "token_type":"example",
       "expires_in":3600,
       "refresh_token":"8xLOxBtZp8"
     }

   Clients SHOULD ignore unrecognized response parameters.  The sizes of
   tokens and is not supported other values received from the authorization server, are
   left undefined by this specification.

5.1.2.  URI Query Parameter

   When including  Clients should avoid making
   assumptions about value sizes.  Servers should document the access token in expected
   size of any value they issue.

5.3.  Error Response

   If the HTTP token request URI, is invalid or unauthorized, the client
   adds authorization
   server constructs the access token response by adding the following parameter to
   the request URI query component as defined
   by [RFC3986] entity body of the HTTP response using the "oauth_token" parameter. "application/json"
   media type:

   error
         REQUIRED.  A single error code as described in Section 5.3.1.

   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.

   For example, example:

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

     {
       "error":"invalid_request"
     }

   If the client makes the following provided invalid credentials using an HTTP
   authentication scheme via the "Authorization" request using
   transport-layer security:

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

   The header field,
   the authorization server MUST respond with the HTTP 401
   (Unauthorized) status code.  Otherwise, the authorization server
   SHALL respond with the HTTP request URI query can include other request-specific
   parameters, in which case, 400 (Bad Request) status code.

5.3.1.  Error Codes

   The authorization server includes one of the "oauth_token" parameters SHOULD be
   appended following error codes
   with the request-specific parameters, properly
   separated by an "&" character (ASCII code 38).

   For example:

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

      NOTE: error response:

   invalid_request
         The "oauth_token" parameter request is used by the previous version
      of the OAuth protocol as described in [RFC5849].  Resource servers
      can differentiate between 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 two protocol versions based on client, or is otherwise malformed.

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

   unauthorized_client
         The authenticated client is REQUIRED in not authorized to use the
      previous version 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).

   unsupported_grant_type
         The access grant included - its type or another attribute - is
         not supported by this specification.

5.1.3.  Form-Encoded Body Parameter

   When including the authorization server.

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

   [[ Add mechanism for extending error codes ]]

6.  Accessing a Protected Resource

   Clients access protected resources by presenting an access token in the HTTP request entity-body, to
   the
   client adds resource server.  The resource server MUST validate the access
   token to the request body using and ensure it has not expired and that its scope covers the
   "oauth_token" parameter.  The client can use this method only if
   requested resource.  The methods used by the
   following REQUIRED conditions resource server to
   validate the access token are met:

   o  The entity-body is single-part.

   o  The entity-body follows beyond the encoding requirements scope of this specification,
   but generally involve an interaction or coordination between 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
   resource server and authorization server.

   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).

   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 utilized the previous version
      of the OAuth protocol as described in [RFC5849].  Resource servers
      can differentiate between access token to
   authenticate with the two protocol versions based resource server depends on the
      presence type of the "oauth_signature_method" which is REQUIRED in the
      previous version and is not supported access
   token issued by this specification.

5.2. the authorization server.

6.1.  Access Token Types

   [[ add token type explanation, maybe with links to other token specs
   ]]

6.2.  The WWW-Authenticate Response Header Field

   If the protected resource request does not include authentication
   credentials, contains an invalid access token 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" "OAuth2" [ RWS token-challenge

     token-challenge 1#param ]

     param           = realm
                       [ CS scope /
                       error ]
                       [ CS / error-desc ]
                       [ CS / error-uri ]
                       [ CS /
                       ( token "=" ( token / quoted-string ) )

     scope ]
                       [ CS 1#auth-param ]           = "scope" "=" <"> scope-v *( SP scope-v ) <">
     scope-v         = 1*quoted-char

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

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

   For example:

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

   The "realm" "scope" attribute is used to provide a space-delimited list of scope values
   indicating the protected resources
   partition as defined by [RFC2617]. [[ add explanation ]] 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 is used to provide the client with the reason why the access
   request was declined.  The parameter values are value is described in
   Section 5.2.1.

   The 6.2.1.  In addition, the resource server MAY include the
   "error_description" attribute provides to provide a human-readable text
   containing additional information, used to assist in the
   understanding
   explanation, and resolution of the error occurred.

   The "error_uri" "error-uri" attribute provides a with an absolute URI
   identifying a human-readable web page with information about the error, used to offer the end-user
   with additional information about explaining the error.  If the value is not an
   absolute URI, it is relative to the URI of the requested protected
   resource.  The "scope"
   "error", "error_description", and "error_uri" attribute is MUST NOT
   appear more than once.

   For example, in response to a space-delimited list of scope values
   indicating the required scope of the protected resource request without
   authentication:

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: OAuth2

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

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: OAuth2
                       error="invalid_token",
                       error_description="The access token for accessing the
   requested resource.

5.2.1. expired"

6.2.1.  Error Codes

   The authorization

   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
   with in 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 SHOULD
         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. expired, revoked, malformed, or
         invalid for other reasons.  The resource server MUST SHOULD 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 MAY
         request a new access token using the
         refresh token issued with and retry the expired access token.  The protected resource server MUST respond with the HTTP 401 (Unauthorized)
         status code.
         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.

   [[ 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. OAuth2

7.  Extensibility

6.1.

7.1.  Defining New Client Credentials Types

   [[ TBD ]]

6.2.

7.2.  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), 9.1), 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
     name-char   = "-" / "." / "_" / DIGIT / ALPHA

6.3.

7.3.  Defining New Header Field Parameters

   Applications that wish to define new parameters for use in the OAuth
   "Authorization" or
   "WWW-Authenticate" header fields field MUST register them in the parameters
   registry, following the procedures in Section 8.1. 9.1.

   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.

7.4.  Defining New Access Grant Types

   The assertion access grant type was designed to allow allows 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.

8.  Security Considerations

   [[ TBD ]]

8.

9.  IANA Considerations

8.1.

9.1.  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 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.

9.1.1.  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.

9.1.2.  Example

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

   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, Bill de hOra, Brian Ellin, Igor Faynberg, George Fletcher,
   Tim Freeman, Evan Gilbert, Kristoffer Gronowski, Justin Hart, Mike
   Jones, John Kemp, Chasen Le Hara, Torsten Lodderstedt, Alastair Mair,
   Eve Maler, James Manger, Laurence Miao, Chuck Mortimore, Justin
   Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre, Marius Scurtescu,
   Naitik Shah, Justin Smith, Jeremy Suriel, and Christian Stuebner, Paul
   Tarjan, Franklin Tse. Tse, and Nick Walker.

Appendix C.  Acknowledgements

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

Appendix D.  Document History

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

   -11

   o  Many editorial changes.  Fixed user authorization section
      structure.  Removed unused normative references.  Adjusted
      language regarding single use of authorization codes.

   o  Fixed header ABNF.

   o  Change access token description from shared symmetric secret to
      password.

   o  Moved access grant 'none' to a separate section, renamed to
      'client_credentials'.

   o  Demoted the HTTP status code requirement from MUST to SHOULD in
      protected resource response error.

   o  Removed 'expired_token' error code.

   o  Moved all the 'code_and_token' parameter to the fragment (from
      code being in the query).

   o  Removed 'assertion_type' parameter (moved to 'grant_type').

   o  Added note about redirecting to invalid redirection URIs (open
      redirectors).

   o  Removed bearer token section, added new required 'token_type'
      parameter with extensibility.

   o  'error-uri' parameter value changed to absolute URI.

   o  OAuth 2.0 HTTP authentication scheme name changed to 'OAuth2'.

   o  Dropped the 'WWW-Authenticate' header field 'realm' parameter.

   o  Removed definition of access token characters.

   o  Added instructions for dealing with error and an invalid
      redirection URI.

   -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.

   o  Added definition for 'access grant'.

   -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 '_'.

   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.

   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.

   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

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

9.

10.  References

9.1.

10.1.  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.

   [RFC2828]  Shirey, R., "Internet Security Glossary", RFC 2828,
              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
              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.

10.2.  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.

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/