Network Working Group                               E. Hammer-Lahav, Ed.
Internet-Draft                                                    Yahoo!
Obsoletes: 5849 (if approved)                                D. Recordon
Intended status: Standards Track                                Facebook
Expires: June 4, July 25, 2011                                          D. Hardt
                                                               Microsoft
                                                        December 1, 2010
                                                        January 21, 2011

                  The OAuth 2.0 Authorization Protocol Framework
                         draft-ietf-oauth-v2-11
                         draft-ietf-oauth-v2-12

Abstract

   This specification describes the OAuth 2.0 protocol framework. authorization protocol.

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 June 4, July 25, 2011.

Copyright Notice

   Copyright (c) 2010 2011 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  3
     1.1.  Notational Conventions  Roles  . . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology . . . . . . .  3
     1.2.  Access Token . . . . . . . . . . . . . . . .  5
     1.3.  Overview . . . . . . .  5
     1.3.  Authorization Grant  . . . . . . . . . . . . . . . . . .  7 .  6
     1.4.  Access Grants  Refresh Token  . . . . . . . . . . . . . . . . . . . . . .  8
       1.4.1.  Authorization Code  7
     1.5.  Notational Conventions . . . . . . . . . . . . . . . . . .  8
       1.4.2.  Resource Owner Password Credentials  9
   2.  Client Authentication  . . . . . . . . . 10
       1.4.3.  Client Credentials . . . . . . . . . . .  9
     2.1.  Client Password Authentication . . . . . . . 10
       1.4.4.  Refresh Token . . . . . . .  9
     2.2.  Other Client Authentication Methods  . . . . . . . . . . . 10
   3.  Protocol Endpoints . . 11
       1.4.5.  Assertion . . . . . . . . . . . . . . . . . . . . 11
     3.1.  Authorization Endpoint . . 12
   2.  Client Profiles . . . . . . . . . . . . . . . . 11
     3.2.  Token Endpoint . . . . . . . 12
     2.1.  Web Server . . . . . . . . . . . . . . . 12
   4.  Requesting an Access Token . . . . . . . . . 12
     2.2.  User-Agent . . . . . . . . . 13
     4.1.  Authorization Code . . . . . . . . . . . . . . . 14
     2.3.  Native Application . . . . . 13
     4.2.  Implicit Grant . . . . . . . . . . . . . . . 15
     2.4.  Autonomous . . . . . . . 19
     4.3.  Resource Owner Password Credentials  . . . . . . . . . . . 24
     4.4.  Client Credentials . . . . . . 16
   3.  Client Credentials . . . . . . . . . . . . . . 26
     4.5.  Extensions . . . . . . . . 17
     3.1.  Client Password Credentials . . . . . . . . . . . . . . . 17
     3.2.  Client Assertion Credentials . 28
   5.  Issuing an Access Token  . . . . . . . . . . . . . . 18
   4.  Obtaining End-User Authorization . . . . . 28
     5.1.  Successful Response  . . . . . . . . . . 20
     4.1.  Authorization Request . . . . . . . . . 28
     5.2.  Error Response . . . . . . . . . 20
     4.2.  Authorization Response . . . . . . . . . . . . . 30
   6.  Refreshing an Access Token . . . . . 22
     4.3.  Error Response . . . . . . . . . . . . . 31
   7.  Accessing Protected Resources  . . . . . . . . . 24
       4.3.1.  Error Codes . . . . . . . 32
     7.1.  Access Token Types . . . . . . . . . . . . . . 25
   5.  Obtaining an Access Token . . . . . . 33
   8.  Extensibility  . . . . . . . . . . . . 25
     5.1.  Access Grant Types . . . . . . . . . . . . 33
     8.1.  Defining Access Token Types  . . . . . . . . 27
       5.1.1.  Authorization Code . . . . . . . 33
     8.2.  Defining New Endpoint Parameters . . . . . . . . . . . 27
       5.1.2.  Resource Owner Password Credentials . . 34
     8.3.  Defining New Authorization Grant Types . . . . . . . 27
       5.1.3.  Client Credentials . . . 34
   9.  Security Considerations  . . . . . . . . . . . . . . . 28
       5.1.4.  Refresh Token . . . . 34
   10. IANA Considerations  . . . . . . . . . . . . . . . . 28
       5.1.5.  Assertion . . . . . 35
     10.1. The OAuth Access Token Type Registry . . . . . . . . . . . 35
     10.2. The OAuth Parameters Registry  . . . . . . 29
     5.2.  Access Token Response . . . . . . . . 36
   Appendix A.  Examples  . . . . . . . . . . 30
     5.3.  Error Response . . . . . . . . . . . . 39
   Appendix B.  Contributors  . . . . . . . . . . 31
       5.3.1.  Error Codes . . . . . . . . . . 39
   Appendix C.  Acknowledgements  . . . . . . . . . . . 32
   6.  Accessing a Protected Resource . . . . . . . 39
   Appendix D.  Document History  . . . . . . . . . 33
     6.1.  Access Token Types . . . . . . . . . 39
   11. References . . . . . . . . . . . 33
     6.2.  The WWW-Authenticate Response Header Field . . . . . . . . 33
       6.2.1.  Error Codes . . . . . . . 43
     11.1. Normative References . . . . . . . . . . . . . . 35
   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  . . . . . . . . . . . 43
     11.2. Informative References . . 37
   8.  Security Considerations . . . . . . . . . . . . . . . . 45
   Authors' Addresses . . . 37
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
     9.1.  The 45

1.  Introduction

   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 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 duration or access to a limited subset of
      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 Parameters Registry  . . . . . . . . . . . . . . 37
       9.1.1.  Registration Template  . . . . . . . . . . . . . . . . 37
       9.1.2.  Example  . . . . . . . . . . . . . . . . . . . . . . . 38
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . . 38
   Appendix B.  Contributors  . . . . . . . . . . . . . . . . . . . . 38
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 39
   Appendix D.  Document History  . . . . . . . . . . . . . . . . . . 39
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 44
     10.2. Informative References . . . . . . . . . . . . . . . . . . 45
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 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 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 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, the client obtains an access token - a string which
   denotes a specific scope, duration, and other attributes.  Access
   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.

   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).

   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 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 [RFC3986]: URI-reference; and from
   [I-D.ietf-httpbis-p1-messaging]: OWS, RWS, and quoted-string.

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

1.2.  Terminology

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

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

   client
         An application obtaining authorization and making protected
         resource requests.

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

   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
         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 4.

   token endpoint
         The authorization server's HTTP endpoint capable of issuing
         tokens and refreshing expired tokens.  The token endpoint is
         described in Section 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 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 addresses these issues by presenting the access
   token to the resource server.

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

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

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

   (A)  The client requests authorization from that of the resource
   owner.  The
        authorization request can be made directly to  In OAuth, the resource
        owner, or preferably indirectly via an intermediary such as an
        authorization server.

   (B)  The client receives an requests access grant which represents to resources controlled
   by the
        authorization provided resource owner and hosted by the resource server, and is
   issued a different set of credentials than those of the resource
   owner.

   (C)  The

   Instead of using the resource owner's credentials to access protected
   resources, the client requests obtains an access token - a string denoting a
   specific scope, duration, and other access attributes.  Access tokens
   are issued to third-party clients by authenticating with the an authorization server using its with the
   approval of the resource owner.  The client credentials, and
        presenting uses the access grant.

   (D)  The authorization server validates token to
   access the client credentials and protected resources hosted by the resource server.

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

1.1.  Roles

   OAuth includes four roles working together to grant and provide
   access token.

   (E) to protected resources - access restricted resources which
   require authentication to access:

   resource owner
      An entity capable of granting access to a protected resource.
      When the resource owner is a person, it is referred to as an end-
      user.
   resource server
      The server hosting the protected resources, capable of accepting
      and responding to protected resource requests using access tokens.
   client makes a
      An application making protected resource request to requests on behalf of the
      resource owner and with its authorization.
   authorization 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 issuing access grant represents tokens to the authorization provided by client after successfully
      authenticating the resource owner.  The access grant type depends on the method used by
   the client owner and supported by obtaining authorization.

   The interaction between the authorization server to obtain it.

1.4.1.  Authorization Code

   The authorization code and resource server
   is an access grant obtained by directing beyond the
   end-user to an authorization server. scope of this specification.  The authorization server
   authenticates
   may be the end-user, obtains authorization, and issues same server as the an resource server or a separate entity.
   A single authorization code to the client.  Because the end-user only
   authenticates server may issue access tokens accepted by
   multiple resource servers.

   When interacting with the authorization server, the end-user's password
   is never shared with the client. client identifies
   itself using a set of client credentials which include a client
   identifier and other authentication attributes.  The authorization code access grant is suitable when means through
   which the client is
   interacting obtains its credentials are beyond the scope of this
   specification, but typically involve registration with an end-user via a user-agent.

     +----------+ the
   authorization server.

     +--------+                               +---------------+
     |        |--(A)- Authorization Request ->|   Resource    |
     | End-User        |                               |     Owner     |
     |        |<-(B)-- Authorization Grant ---|               |
     |
     +----------+
          ^        |
         (B)
     +----|-----+        Client Identifier                               +---------------+
     |         -+--(A)--- & Redirect URI ----->|        |
     |  User-        |        Authorization Grant &  +---------------+
     |        |--(C)--- Client Credentials -->| Authorization |
     |  Agent  -|--(B)-- User authenticates -->| Client |                               |     Server    |
     |        |<-(D)----- Access Token -------|               |
     |        |                               +---------------+
     |        |
     |         -+--(C)-- Authorization Code --<|        |
     +-|----|---+                               +---------------+
      (A)  (C)
     |        |--(E)----- Access Token ------>|    Resource   |
       ^    v
     +---------+
     |        |                               |  Client     Server    |
     |        |<-(F)--- Protected Resource ---|               |
     +---------+
     +--------+                               +---------------+
                     Figure 2: Obtaining an Authorization Code 1: Abstract Protocol Flow

   The authorization code abstract flow illustrated in Figure 2 1 describes the interaction
   between the four roles and includes the following steps:

   (A)  The client initiates the flow by directing requests authorization from the end-user's user-
        agent resource owner.  The
        authorization request can be made directly to the resource owner
        (as shown), or preferably indirectly via an intermediary such as
        an authorization server's end-user server.
   (B)  The client receives an authorization
        endpoint. grant which represents the
        authorization provided by the resource owner.  The authorization
        grant type depends on the method used by the client and
        supported by the authorization server to obtain it.
   (C)  The client includes requests an access token by authenticating with the
        authorization server using its client identifier, requested
        scope, local state, credentials (prearranged
        between the client and a redirection URI (to which authorization server) and presenting the
        authorization grant.
   (D)  The authorization server will send validates the user-agent back once client credentials and
        the authorization grant, and if valid issues an access
        is granted or denied).

   (B) token.
   (E)  The authorization server authenticates client requests the end-user (via protected resource from the
        user-agent) resource
        server and establishes whether authenticates by presenting the end-user grants or
        denies access token.
   (F)  The resource server validates the client's access token, and if valid,
        serves the request.

   (C)  If

1.2.  Access Token

   An access token is granted, the a string representing an authorization server directs issued to
   the user-
        agent back client.  The string is usually opaque to the client using client.  Tokens
   represent specific scopes and durations of access, granted by the redirection URI provided.
        The authorization
   resource owner, and enforced by the resource server includes and authorization
   server.

   The token may denote an identifier used to retrieve the authorization code
   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.  Additional
   authentication credentials may be required in order for the client to
   use to obtain an access a token.

   Once the client obtains

   The access token provides an abstraction layer, replacing different
   authorization code, it requests an access constructs (e.g. username and password) with a single
   token understood by authenticating with the authorization server (using its
   client credentials) and presenting resource server.  This abstraction enables
   issuing access tokens more restrictive than the authorization code (access
   grant).

   In cases where the client is incapable of maintaining its client
   credentials secret (such grant
   used to obtain them, as native applications or an application
   implemented well as removing the resource server's need
   to understand a user-agent script), wide range of authentication methods.

   Access tokens can have different formats, structures, and methods of
   utilization (e.g. cryptographic properties) based on the authorization resource
   server issues
   an access security requirements.  Access token directly attributes and the
   methods used to access protected resources are beyond the client in step (C), instead scope of
   issuing an authorization code.

   Obtaining an
   this specification and are defined by companion specifications.

1.3.  Authorization Grant

   An authorization code grant is described in Section 4.

1.4.2.  Resource Owner Password Credentials

   The resource owner password credentials (e.g. a username and
   password) can be general term used directly as an access grant to obtain an access
   token.  The describe the
   intermediate credentials should only be used when there is a high
   degree of trust between representing the resource owner
   authorization, and serves as an abstraction layer.  An authorization
   grant is used by the client (e.g. its
   computer operating system or a highly privileged application), and
   when other to obtain an access grant types are not available (such as token.

1.3.1.  Authorization Code

   The authorization code is obtained by using an authorization code).

   Even though this grant type requires direct server
   as an intermediary between the client access to and resource owner.  Instead of
   requesting authorization directly from the resource owner's credentials, owner, the client
   directs the resource owner's credentials are
   used for a single request and are exchanged for owner to an access token.
   Unlike the HTTP Basic authentication scheme defined authorization server (via its user-
   agent), which in [RFC2617],
   this grant type eliminates turns directs the need for resource owner back to the client to store
   with the
   resource-owner's credentials for future use.

   In Figure 3, authorization code.

   Before directing the resource owner back to the client requests with the
   authorization from code, the authorization server authenticates the
   resource owner directly.  When and obtains authorization.  Because the resource owner is an end-user,
   only authenticates with the client
   typically prompts authorization server, the end-user for resource
   owner's credentials are never shared with the username and password.

     +--------+                               +----------+
     |        |--(A)- Authorization Request ->| Resource |
     | Client |                               |   Owner  |
     |        |<-(B)-- Username & Password ---|          |
     +--------+                               +----------+

          Figure 3: Obtaining Resource Owner Password Credentials

1.4.3.  Client Credentials client.

   The client credentials can be used authorization code provides a few important security benefits
   such as an access grant when the
   authorization scope is limited ability to authenticate the protected resources under client and issuing the
   control of access
   token directly to the client, or other protected resources previously
   arranged with client without potentially exposing it to
   others, including the resource owner.

1.3.2.  Implicit

   An implicit grant is issued when the resource owner's authorization server.  Client credentials are used
   is expressed directly as an access token, without using an
   intermediate credential.  The implicit grant typically when is issued in a similar
   manner as an authorization code, but instead of the resource owner
   being redirected back to the client with the authorization code, it
   is acting on redirected back with an access token and 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. related attributes.

   When issuing an access token, implicit grant, the authorization server can include a refresh token which is used by cannot
   verify the client to
   obtain a new access token when identity of the current access token expires.
   When requesting a new access token, client, and the refresh token acts as an access grant.  Using a refresh token removes the need may be
   exposed to interact
   with the resource owner again, or other applications with access to store
   the original access grant
   used resource owner's user-agent.

   Implicit grants improve the responsiveness and efficiency of some
   clients (such as a client implemented as an in-browser application)
   since it reduces the number of round trip required to obtain the an
   access token and refresh token.

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

1.3.3.  Resource ---|    Resource   |
     | Client |                              |     Server    |
     |        |--(E)----- Access Token ----->|               |
     |        |                              |               |
     |        |<-(F)-- Invalid Token Error --|               |
     |        |                              +---------------+
     |        |
     |        |          Refresh Token &     +---------------+
     |        |--(G)-- Client Owner Password Credentials -->| Authorization |
     |        |                              |     Server    |
     |        |<-(H)----- Access Token ------|               |
     +--------+     & Optional Refresh Token +---------------+

                   Figure 4: Refreshing an Access Token

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

   (A)

   The client requests resource owner password credentials (e.g. a username and
   password) can be used directly as an access token by authenticating with the authorization server using its client credentials, and
        presenting grant to obtain an
   access grant.

   (B) token.  The authorization server validates the client credentials should only be used when there is a
   high degree of trust between the resource owner and the access grant, client (e.g.
   its computer operating system or a highly privileged application),
   and if valid issues when other authorization grant types are not available (such as
   an access token and a
        refresh token.

   (C)  The authorization code).

   Even though this grant type requires direct client makes a protected resource requests access to the
   resource
        server by presenting owner credentials, the resource owner credentials are used
   for a single request and are exchanged for an access token.

   (D)  The resource server validates  Unlike
   the access token, and if valid,
        serves HTTP Basic authentication scheme defined in [RFC2617], this grant
   type eliminates the request.

   (E)  Steps (C) and (D) repeat until need for the access token expires.  If client to store the resource-owner
   credentials for future use.

1.3.4.  Client Credentials

   The client does not know credentials can be used as an authorization grant when the
   authorization scope is limited to the access token expired, it makes another protected resource request.  Otherwise, it skips resources under the
   control of the client, or to step (G).

   (F)  Since protected resources previously arranged
   with the access token authorization server.  Client credentials are used as an
   authorization grant typically when the client is invalid (expired), acting on its own
   behalf (the client is also the resource server
        returns an invalid token error.

   (G)  The client requests owner).

1.3.5.  Extensions

   Additional grant types may be defined to provide a bridge between
   OAuth and other trust frameworks.  For example,
   [I-D.ietf-oauth-saml2-bearer] defines a new SAML 2.0
   [OASIS.saml-core-2.0-os] bearer assertion grant type, which can be
   used to obtain an access token.

1.4.  Refresh Token

   A refresh token is optionally issued by authenticating with the authorization server using its client credentials, and
        presenting the refresh token (as to
   the client together with an access grant).

   (H) token.  The authorization server validates the client credentials and can use the
   refresh token, and if valid issues a new token to request another access token (and
        optionally, a new refresh token).

1.4.5.  Assertion

   Assertions provide a bridge between OAuth and other trust frameworks.
   They enable based on the client same
   authorization, without having to utilize existing trust relationships in
   order involve the resource owner again, or
   having to retain the original authorization grant used to obtain an the
   initial access token.  The access grant represented

   A refresh token is a string representing the authorization granted to
   the client by an
   assertion depends on the assertion type, its content, and how it was
   issued, which are beyond resource owner.  The string is usually opaque to
   the scope of this specification.

   Assertions are client.  The token may denote an identifier used as part of to retrieve the protocol extensibility model,
   providing a way for
   authorization servers to support additional
   access grant types.

2.  Client Profiles

   [[ add intro and find new names for information, or self-contain the profiles. this section will
   have normative language authorization
   information in future drafts, similar to -05 and earlier.
   ]]

2.1.  Web Server a verifiable manner.

   The web server profile is suitable for clients capable of interacting
   with refresh token can be used to obtain a new access token when the end-user's user-agent (typically
   current access token expires (access tokens may have a web browser) and capable
   of receiving incoming requests (via redirection) from shorter
   lifetime than authorized by the
   authorization server (capable of acting as an HTTP server).

     +----------+          Client Identifier resource owner), or to obtain
   additional access tokens with identical or narrower scope.

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

               Figure 5: Web Server Flow 2: Refreshing an Expired Access Token

   The web server flow illustrated in Figure 5 2 includes the following steps:

   (A)  The web client initiates requests an access token by authenticating with the flow
        authorization server using its client credentials, and
        presenting an authorization grant.
   (B)  The authorization server validates the client credentials and
        the authorization grant, and if valid issues an access token and
        a refresh token.
   (C)  The client makes a protected resource requests to the resource
        server by redirecting presenting the end-user's
        user-agent access token.

   (D)  The resource server validates the access token, and if valid,
        serves the request.
   (E)  Steps (C) and (D) repeat until the access token expires.  If the
        client knows the access token expired, it skips to step (G),
        otherwise it makes another protected resource request.
   (F)  Since the end-user authorization endpoint as described
        in Section 4. access token is invalid (expired), the resource server
        returns an invalid token error.
   (G)  The client includes its client identifier,
        requested scope, local state, and requests a redirect URI to which new access token by authenticating with
        the authorization server will send using its client credentials, and
        presenting the end-user back once access is
        granted (or denied).

   (B) refresh token.
   (H)  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 refresh token, and if valid issues a new access request.

   (C)  Assuming token (and
        optionally, a new refresh token).

1.5.  Notational Conventions

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

   This specification uses the end-user granted access, Augmented Backus-Naur Form (ABNF)
   notation of [I-D.ietf-httpbis-p1-messaging].  Additionally, the authorization server
        redirects
   following rules are included from [RFC3986]: URI-reference; and from
   [I-D.ietf-httpbis-p1-messaging]: OWS, RWS, and quoted-string.

   Unless otherwise noted, all the user-agent back protocol parameter names and values
   are case sensitive.

2.  Client Authentication

   Client credentials are used to identify and authenticate the client.
   The client credentials include a client identified - a unique string
   issued to the redirection
        URI provided earlier.  The authorization includes an
        authorization code for the client to use identify itself to obtain an access
        token.

   (D) the authorization server.
   The methods through which the client requests an access token from obtains its client credentials
   are beyond the authorization
        server by authenticating and including scope of this specification.

   Due to the authorization code
        received in nature of some clients, the previous step as described in Section 5.

   (E)  The authorization server validates SHOULD
   NOT make assumptions about the confidentiality of client credentials and
        the authorization code and responds back credentials
   without establishing trust with the access token.

2.2.  User-Agent client.  The user-agent profile is suitable for authorization server
   SHOULD NOT issue client applications residing
   in a user-agent, typically implemented in a browser using a scripting
   language such as JavaScript.  These credentials to clients cannot keep client incapable of keeping
   their secrets confidential and the confidential.

2.1.  Client Password Authentication

   The client password authentication of uses a shared symmetric secret to
   authenticate the client.  The client is based on
   the user-agent's same-origin policy.

   Unlike other profiles identifier and password are
   included in which the request using the following parameters:

   client_id
         REQUIRED.  The client makes separate requests identifier.
   client_secret
         REQUIRED.  The client password.

   For example (line breaks are for
   end-user authorization and access token, the 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

2.2.  Other Client Authentication Methods

   In cases where client receives the
   access token as a result of password authentication is not suitable or
   sufficient, the end-user authorization request in the
   form of an server MAY support other existing HTTP redirection.  The client requests
   authentication schemes or define new methods.  In addition, the
   authorization server to redirect MAY allow unauthenticated access token requests
   when the user-agent to another web server client identity does not matter (e.g. anonymous client) or local
   resource accessible to
   when the user-agent which client identity is capable of extracting established via other means.

   For example, the access token from authorization server MAY support using the response and passing it HTTP
   Basic authentication scheme as defined in [RFC2617] to include the client.

   This user-agent profile does not utilize
   client identifier as the username and client secret since password as the password
   (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&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

   When using a method other than client executables reside on password authentication to
   exchange an authorization code grant type, the end-user's computer or device which
   makes authorization server
   MUST define a method for mapping the client secret accessible and exploitable.  Because the
   access token is encoded into the redirection URI, it may be exposed credentials to the end-user and other applications residing on the computer or
   device.

          +----------+          Client Identifier     +----------------+
          |          |>---(A)-- & Redirection URI --->|                |
          |          |                                |                |
   End <--+  -  -  - +----(B)-- User authenticates -->|  Authorization |
   User   |          |                                |     Server     |
          |          |<---(C)--- Redirect URI -------<|                |
          |  Client  |         with Access Token      |                |
          |    in    |            in Fragment         +----------------+
          |  Browser |
          |          |                                +----------------+
          |          |>---(D)--- Redirect URI ------->|                |
          |          |         without Fragment       |   Web Server   |
          |          |                                |   with Client  |
          |    (F)   |<---(E)--- Web Page with ------<|    Resource    |
          |  Access  |              Script            |                |
          |   Token  |                                +----------------+
          +----------+
                         Figure 6: User-Agent Flow

   The user-agent flow illustrated in Figure 6 includes client
   identifier used to obtain the following
   steps:

   (A) authorization code.

3.  Protocol Endpoints

   The client sends authorization process utilizes two endpoints:

   o  Authorization endpoint - used to obtain authorization from the
      resource owner via user-agent redirection.
   o  Token endpoint - used to the end-user exchange an authorization
        endpoint grant for an
      access token, typically with client authentication.

   Not every authorization grant flow utilizes both endpoints.
   Extension grant types MAY define additional endpoints as described in Section 4. needed.

3.1.  Authorization Endpoint

   The client includes its
        client identifier, requested scope, local state, and a redirect
        URI authorization endpoint is used to which interact with the resource
   owner and obtain authorization which is expressed explicitly as an
   authorization code (exchanged for an access token), or implicitly by
   direct issuance of an access token.

   The authorization server will send MUST first verify the end-user
        back once authorization is granted (or denied).

   (B) identity of the
   resource owner.  The way in which the authorization server
   authenticates the end-user (via the
        user-agent) resource owner (e.g. username and establishes whether the end-user grants or
        denies the client's access request.

   (C)  If password login,
   session cookies) is beyond the end-user granted access, scope of this specification.

   The location of the authorization server
        redirects the user-agent to endpoint can be found in the redirection URI provided
        earlier.
   service documentation.  The redirection endpoint URI includes MAY include a query
   component as defined by [RFC3986] section 3, which MUST be retained
   when adding additional query parameters.

   Requests to the access token authorization endpoint result in user authentication
   and the
        URI fragment.

   (D)  The user-agent follows transmission of sensitive information.  If the redirection instructions by making a
        request to response
   includes an access token, the web authorization server which MUST require TLS
   1.2 as defined in [RFC5246] and MAY support additional transport-
   layer mechanisms meeting its security requirements.  If the response
   does not include an access token, the fragment.
        The user-agent retains the fragment information locally.

   (E) authorization server SHOULD
   require TLS 1.2 and any additional transport-layer mechanism meeting
   its security requirements.

   The web authorization server returns a web page (typically an HTML page with
        an embedded script) capable of accessing MUST support the full redirection
        URI including use of the fragment retained by HTTP "GET"
   method for the user-agent, authorization endpoint, and
        extracting MAY support the access token (and other parameters) contained in use of the fragment.

   (F)
   "POST" method as well.

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

3.1.1.  Redirection URI

   The user-agent executes the script provided by client directs the web server
        locally, which extracts resource owner's user-agent to the access token
   authorization endpoint and passes it includes a redirection URI to which the
        client.

2.3.  Native Application

   Native applications are clients running as native code on
   authorization server will redirect the end-
   user's computer or device (i.e. executing outside a user-agent or as
   a desktop program).  These clients are often capable of interacting
   with back once
   authorization has been obtained (or embedding) denied).  The client MAY omit 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
   redirection URI if one has been established between the server (e.g. firewall, operating system
   restrictions).

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

   o  Utilize the end-user
   authorization endpoint server via other means, such as described in
      Section 4 by launching an external user-agent.  The client can
      capture during the response by providing a client
   registration process.

   The redirection URI with a custom MUST be an absolute URI scheme (registered with and MAY include a query
   component, which MUST be retained by the operating system to invoke authorization server when
   adding additional query parameters.

   The authorization server SHOULD require the client application), to pre-register
   their redirection URI or by providing at least certain components such as the
   scheme, host, port and path.  If a redirection URI pointing to
      a server-hosted resource under was registered,
   the client's control which makes authorization server MUST compare any redirection URI received at
   the response available to authorization endpoint with the client (e.g. using registered URI.

   The authorization server SHOULD NOT redirect the window title user-agent to
   unregistered or other locations accessible from outside untrusted URIs to prevent the user-agent).

   o  Utilize endpoint from being
   used as an open redirector.  If no valid redirection URI is
   available, the end-user authorization server SHOULD inform the resource owner
   directly of the error.

3.2.  Token Endpoint

   The token endpoint as described in
      Section 4 is used by using an embedded user-agent.  The client obtains the
      response client to obtain an access token by directly communicating
   authenticating with the embedded user-agent.

   o  Prompt end-users for their password authorization server and use them directly to
      obtain presenting its
   authorization grant.  The token endpoint is used with every
   authorization grant except for the implicit grant type (since an
   access token.  This token is generally discouraged, as it
      hands issued directly).

   The location of the end-user's password directly to token endpoint can be found in the third-party client service
   documentation.  The endpoint URI MAY include a query component, which in turn has
   MUST be retained when adding additional query parameters.

   Since requests to store it in clear-text.  It also requires the
      server to support password-based authentication.

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

   o  External user-agents may improve completion rate as transmission of
   clear-text credentials (in the end-user
      may already be logged-in HTTP request and not have to re-authenticate.

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

   o  Embedded user-agents pose
   authorization server MUST require the use of a transport-layer
   security challenge because users are
      authenticating in an unidentified window without access mechanism when sending requests to the
      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 token endpoints.  The
   authorization server MUST support TLS 1.2 as defined in different ways based on their requirements [RFC5246],
   and MAY support additional transport-layer mechanisms meeting its
   security requirements.

   The token endpoint requires client authentication as described in
   Section 2 .  The authorization server MAY accept any form of client
   authentication meeting its security requirements.  The client MUST
   NOT use more than one authentication method in each request.

   The client MUST use the
   existing trust framework they rely upon.  Autonomous clients can:

   o  Obtain an HTTP "POST" method when making access token by authenticating with
   requests.

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

4.  Requesting an Access Token

   The scope of the client obtains an access token is limited to the protected resources under the control of by requesting authorization from
   the client, or that of another resource owner previously arranged
      with owner.  The authorization is expressed in the form of an
   authorization server.

   o  Use grant which the client exchanges for an existing access token.
   OAuth defines four grant expressed types: authorization code, implicit,
   resource owner password credentials, and client credentials, as well
   as an assertion using an
      assertion format supported by extension mechanism for defining additional grant types.

4.1.  Authorization Code

   The authorization code flow is suitable for clients capable of
   maintaining their client credentials confidential (for authenticating
   with the authorization server) such as a client implemented on a
   secure server.  Using
      assertions requires  As a redirection-based profile, the client to obtain an assertion (such as must be
   capable of interacting with the resource owner's user-agent
   (typically a
      SAML [OASIS.saml-core-2.0-os] assertion) web browser) and capable of receiving incoming requests
   (via redirection) from an assertion issuer
      or to self-issue an assertion. the authorization server.

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

                     Figure 3: Authorization Code Flow

   The assertion format, the process
      by which the assertion is obtained, and flow illustrated in Figure 3 includes the method of validating following steps:

   (A)  The client initiates the assertion are defined flow by directing the assertion issuer and the
      authorization server, and are beyond the scope of this
      specification.

3.  Client Credentials

   When interacting with resource owner's
        user-agent to the authorization server, the client identifies
   itself using a set of client credentials which include a client
   identifier and other properties for client authentication. endpoint.  The means
   through which the client obtains includes
        its credentials are beyond the scope
   of this specification, but typically involve registration with the
   authorization server.

   Due client identifier, requested scope, local state, and a
        redirection URI to which the nature of some clients, authorization servers SHOULD NOT
   make assumptions about the confidentiality of client secrets without
   establishing trust with server will send the client.  Authorization servers SHOULD NOT
   issue client secrets to clients incapable of keeping their secrets
   confidential.
        user-agent back once access is granted (or denied).
   (B)  The authorization server MAY authenticate authenticates the client using any
   appropriate set of credentials and authentication schemes.  The
   client MUST NOT include more than one set of credentials or
   authentication mechanism with each request.

3.1.  Client Password Credentials

   The client password credentials use a shared symmetric secret to
   authenticate resource owner (via
        the client.  The client identifier user-agent) and password are
   included in the request using the HTTP Basic authentication scheme as
   defined in [RFC2617] by including establishes whether the client identifier as resource owner
        grants or denies the
   username and client password as client's access request.
   (C)  Assuming 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&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

   Alternatively, resource owner grants access, the client MAY include authorization
        server redirects the password in user-agent back to the request
   body client using the following parameters:

   client_id
         REQUIRED.
        redirection URI provided earlier.  The client identifier.

   client_secret  REQUIRED. redirection URI includes
        an authorization code.

   (D)  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 requests an access token from the client credentials authorization
        server's token endpoint by authenticating using
   both the request parameter, its client
        credentials, and includes the HTTP Basic authentication scheme. authorization code received in the
        previous step.
   (E)  The authorization server MAY support additional authentication
   schemes suitable for validates the transmission of password credentials.

3.2.  Client Assertion Credentials

   The client assertion credentials are used in cases where a password
   (clear-text shared symmetric secret) is unsuitable or does not
   provide sufficient security for client authentication.  In such cases
   it is common to use other mechanisms such as HMAC or digital
   signatures that do not require sending clear-text secrets. and
        the authorization code and if valid, responds back with an
        access token.

4.1.1.  Authorization Request

   The client assertion credentials provide an extensible mechanism constructs the request URI by adding the following
   parameters to use
   an assertion the query component of the authorization endpoint URI
   using the "application/x-www-form-urlencoded" format supported as defined by
   [W3C.REC-html401-19991224]:

   response_type
         REQUIRED.  Value MUST be set to "code".
   client_id
         REQUIRED.  The client identifier as described in Section 2.
   redirect_uri
         REQUIRED, unless a redirection URI has been established between
         the client and authorization server for
   authentication the client.

   Using assertions requires via other means.  Described
         in Section 3.1.1.
   scope
         OPTIONAL.  The scope of the client to obtain an assertion (such access request expressed as a SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
   or to self-issue an assertion. list
         of space-delimited strings.  The assertion format, the process by
   which the assertion value is obtained, and the method of validating the
   assertion are defined by the assertion issuer and the
         authorization
   server, server.  If the value contains multiple space-
         delimited strings, their order does not matter, and are beyond each string
         adds an additional access range to the scope of this specification.

   When using a client assertion, requested scope.
   state
         OPTIONAL.  An opaque value used by the client includes to maintain state
         between the following
   parameters:

   client_assertion_type  REQUIRED. request and callback.  The format of the assertion as
         defined by the authorization server.  The server
         includes this value MUST be an
         absolute URI.

   client_assertion  REQUIRED. when redirecting the user-agent back to the
         client.

   The client assertion. directs the resource owner to the constructed URI using an
   HTTP redirection response, or by other means available to it via the
   user-agent.

   For example, the client sends directs the user-agent to make the following access token
   HTTP request using a SAML 2.0 assertion to authenticate itself transport-layer security (line breaks are for
   display purposes only):

     POST /token

     GET /authorize?response_type=code&client_id=s6BhdRkqt3&
         redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb 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

   The authorization server validates the request to ensure all required
   parameters are present and valid.  If the request is valid, the
   authorization server authenticates the resource owner and obtains an
   authorization decision (by asking the resource owner or by
   establishing approval via other means).

   When obtaining a decision is established, the authorization server directs the
   user-agent to the provided client redirection URI using an HTTP
   redirection response, or by other means available to it via the user-
   agent.

4.1.2.  Authorization Response

   If the resource owner grants the access token using a client assertion together with request, the authorization
   server issues an authorization code (as described in Section 5.1.1), a mechanism is
   needed and delivers it to map between the value of "client_id" parameter used client by
   adding the following parameters to
   obtain the query component of the
   redirection URI using the "application/x-www-form-urlencoded" format:

   code
         REQUIRED.  The authorization code, and code generated by the client assertion.  Such
   mechanism
         authorization server.  The authorization code SHOULD expire
         shortly after it is beyond issued to minimize the out risk of scope for this specification, but MUST
   be specified for any leaks.  The
         client assertion type used in combination with MUST NOT reuse the authorization code.  If an
         authorization code is used more than once, the authorization
         server MAY revoke all tokens previously issued based on that
         authorization code.  The authorization server MUST reject access token requests using code is bound to the
         client assertion credentials that do not contain HMAC or signed
   values that:

   o  State identifier and redirection URI.
   state
         REQUIRED if the assertion "state" parameter was specifically issued present in the client
         authorization request.  Set to be consumed by the
      receiving endpoint (typically via an audience or recipient exact value
      containing the receiving endpoint's identifier).

   o  Identify the entity that issued received from
         the assertion (typically via an
      issuer value).

   o  Identify when client.

   For example, the assertion expires as an absolute time (typically
      via an expiration value containing a UTC date/time value).  The authorization server MUST reject expired assertions.

4.  Obtaining End-User Authorization

   Before redirects the user-agent by
   sending the following HTTP response:

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

   The client can access a protect resource, it MUST first obtain SHOULD ignore unrecognized response parameters.  The
   authorization code string size is left undefined by this
   specification.  The clients should avoid making assumptions about
   code value sizes.  The authorization from the end-user.  To obtain an end-user
   authorization, server should document the client sends size
   of any value is issues.

4.1.2.1.  Error Response

   If the end-user request fails due to a missing, invalid, or mismatching
   redirection URI, the end-user authorization endpoint.  Once obtained, server SHOULD inform the end-user access grant is
   expressed as an authorization code which resource
   owner of the client uses to obtain an
   access token.

   At error, and MUST NOT redirect the end-user authorization endpoint, user-agent to the end-user first
   authenticates with
   invalid redirection URI.

   If the authorization server, and then grants or resource owner denies the access request.  The way in which the authorization server
   authenticates request or if the end-user (e.g. username and password login, OpenID,
   session cookies) and in which request
   fails for reasons other than a missing or invalid redirection URI,
   the authorization server obtains informs the
   end-user's authorization, including whether it uses a secure channel
   such as TLS, is beyond client by adding the scope following
   parameters to the query component of this specification.  However, the
   authorization server MUST first verify redirection URI using the identity of
   "application/x-www-form-urlencoded" format:

   error
         REQUIRED.  A single error code from the end-user. following:
         invalid_request
               The location of the end-user request is missing a required parameter, includes an
               unsupported parameter or parameter value, or is otherwise
               malformed.
         invalid_client
               The client identifier provided is invalid.
         unauthorized_client
               The client is not authorized to request an authorization endpoint can be found in
               code using this method.
         access_denied
               The resource owner or authorization server denied the service documentation.
               request.
         unsupported_response_type
               The end-user authorization endpoint URI
   MAY include a query component as defined by [RFC3986] section 3,
   which must be retained when adding server does not support obtaining an
               authorization code using this method.
         invalid_scope
               The requested scope is invalid, unknown, or malformed.
   error_description
         OPTIONAL.  A human-readable text providing additional query parameters.

   Since requests
         information, used to the end-user authorization endpoint result assist in user
   authentication and the transmission understanding and resolution
         of sensitive information, the
   authorization server SHOULD require the use of error occurred.
   error_uri
         OPTIONAL.  A URI identifying a transport-layer
   security mechanism such as TLS when sending requests human-readable web page with
         information about the error, used to provide the resource owner
         with additional information about the error.
   state
         REQUIRED if the "state" parameter was present in the end-user client
         authorization endpoint.

4.1.  Authorization Request

   In order request.  Set to direct the end-user's user-agent to exact value received from
         the authorization
   server, client.

   For example, the client constructs authorization server redirects the request URI user-agent by adding
   sending the following
   parameters HTTP response:

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

4.1.3.  Access Token Request

   The client makes a request to the end-user authorization token endpoint URI query component by adding the
   following parameter using the "application/x-www-form-urlencoded"
   format as defined by
   [W3C.REC-html401-19991224]:

   response_type in the HTTP request entity-body:

   grant_type
         REQUIRED.  The requested response: an access token, an
         authorization code, or both.  The parameter value  Value MUST be set to "token" for requesting an access token, "code" for
         requesting an authorization code, or "code_and_token" to
         request both. "authorization_code".
   code
         REQUIRED.  The authorization server MAY decline to provide
         one or more of these response types.

   client_id code received from the
         authorization server.
   redirect_uri
         REQUIRED.  The redirection URI used in the initial request.

   The client identifier includes its authentication credentials as described in
   Section 3.

   redirect_uri
         REQUIRED, unless a redirection URI has been established between 2

   For example, the client and authorization server makes the following HTTP request by including
   its client credentials via other means.  An
         absolute URI to which the "client_id" and "client_secret"
   parameters, 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 will redirect MUST:

   o  Validate the user-agent to when client credentials and ensure they match the end-user authorization step is
         completed.  The
      authorization server SHOULD require code.
   o  Verify that the client
         to pre-register their authorization code and redirection URI.

   scope
         OPTIONAL.  The scope of URI are valid
      and match its stored association.

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

   state
         OPTIONAL.  An opaque value used by the client to maintain state
         between the request token and callback. optional refresh token, and responds as
   described in Section 5.

4.2.  Implicit Grant

   The implicit grant flow is suitable for clients incapable of
   maintaining their client credentials confidential (for authenticating
   with the authorization server
         includes this value when redirecting server) such as client applications residing
   in a user-agent, typically implemented in a browser using a scripting
   language such as JavaScript, or native applications.  These clients
   cannot keep client secrets confidential and the user-agent back to authentication of the
         client.

   The
   client directs is based on the end-user to user-agent's same-origin policy.

   As a redirection-based profile, the constructed URI using an HTTP
   redirection response, or by other means available to it via client must be capable of
   interacting with the resource owner's user-agent (typically a web
   browser) and capable of receiving incoming requests (via redirection)
   from the end-
   user's user-agent.  The authorization server MUST support server.

   Unlike the use of authorization code flow in which the HTTP "GET" method client makes separate
   requests for the end-user authorization endpoint, and
   MAY support access token, the use of client receives the "POST" method
   access token as well.

   For example, the result of the authorization request.

   The implicit grant flow does not utilize the client directs credentials since
   the end-user's user-agent client is unable to make maintain their confidentiality (the client
   resides on 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 resource owner's computer or device which makes the
   client has previously registered a redirection URI with the
   authorization server, credentials accessible and exploitable).  Because the authorization server MUST verify that access
   token is encoded into the redirection URI received matches URI, it may be exposed to the registered
   resource owner and other applications residing on its computer or
   device.

     +----------+
     | Resource |
     |  Owner   |
     |          |
     +----------+
          ^
          |
         (B)
     +----|-----+          Client Identifier     +---------------+
     |         -+----(A)--- & Redirect URI associated ----->|               |
     |  User-   |                                | Authorization |
     |  Agent  -|----(B)-- User authenticates -->|     Server    |
     |          |                                |               |
     |          |<---(C)---- Redirect URI ------<|               |
     |          |          with
   the client identifier.  The authorization server SHOULD NOT redirect
   the user-agent to unregistered or untrusted URIs to prevent the
   endpoint from being used as an open redirector.  If no valid
   redirection Access Token     +---------------+
     |          |            in Fragment
     |          |                                +---------------+
     |          |----(D)---- Redirect URI is available, the authorization server SHOULD inform ------>|   Web Server  |
     |          |          without Fragment      |  with Client  |
     |          |                                |   Resource    |
     |     (F)  |<---(E)------- Script ---------<|               |
     |          |                                +---------------+
     +-|--------+
       |    |
      (A)  (G) Access Token
       |    |
       ^    v
     +---------+
     |         |
     |  Client |
     |         |
     +---------+

                       Figure 4: Implicit Grant Flow

   The flow illustrated in Figure 4 includes the end-user of following steps:

   (A)  The client initiates the error occured. [[ provide guidance on how flow by directing the resource owner's
        user-agent to
   perform matching ]]

   Parameters sent without a value MUST be treated as if they were
   omitted from the request. authorization endpoint.  The client includes
        its client identifier, requested scope, local state, and a
        redirection URI to which the authorization server SHOULD ignore
   unrecognized request parameters. will send the
        user-agent back once access is granted (or denied).
   (B)  The authorization server validates authenticates the request to ensure all required
   parameters are present resource owner (via
        the user-agent) and valid.  If establishes whether the request is invalid, resource owner
        grants or denies the client's access request.

   (C)  Assuming the resource owner grants access, the authorization
        server redirects the user-agent back to the client using the
        redirection URI provided with earlier.  The redirection URI includes
        the appropriate error code as
   described access token in Section 4.3.

   The authorization server authenticates the end-user and obtains an
   authorization decision (by asking URI fragment.
   (D)  The user-agent follows the end-user or redirection instructions by establishing
   approval via other means).  When making a decision has been established,
        request to the
   authorization web server directs (does not include the end-user's fragment).  The
        user-agent to retains the
   provided client redirection URI using fragment information locally.
   (E)  The web server returns a web page (typically an HTTP HTML document
        with an embedded script) capable of accessing the full
        redirection response,
   or by other means available to it via URI including the end-user's user-agent.

4.2.  Authorization Response

   If fragment retained by the end-user grants user-
        agent, and extracting the access request, token (and other parameters)
        contained in the authorization fragment.
   (F)  The user-agent executes the script provided by the web server
   issues an
        locally, which extracts the access token, an authorization code, or both, token and delivers
   them passes it to the
        client.

4.2.1.  Authorization Request

   The client constructs the request URI by adding the following
   parameters to the
   redirection query component of the authorization endpoint URI (as described below):

   code
         REQUIRED if
   using the response type is "code" or "code_and_token",
         otherwise "application/x-www-form-urlencoded" format:

   response_type
         REQUIRED.  Value MUST NOT be included.  The authorization code
         generated by the authorization server.  The authorization code
         SHOULD expire shortly after it is issued set to minimize the risk
         of leaks. "token".
   client_id
         REQUIRED.  The client MUST NOT reuse the authorization code.
         If an authorization code is used more than once, the
         authorization server MAY revoke all tokens previously issued
         based on that authorization code.  The authorization code is
         bound identifier as described in Section 2.
         Due to lack of client authentication, the client identifier and redirection URI.

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

   token_type
         REQUIRED if the response includes an access token.  The type of
         the token issued.  The token type informs the relied upon for client how the
         access token is to be used when accessing identification.
   redirect_uri
         REQUIRED, unless a protected resource
         as described in Section 6.1.

   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 redirection URI has been established between
         the client and authorization server. server via other means.  Described
         in Section 3.1.1.
   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 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 access range to the one requested by the client. scope.
   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 resource owner 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
   user-agent.

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

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

   The authorization server validates the "response_type"
   parameter. request to ensure all required
   parameters are present and valid.  If the response type request is "code", valid, the
   authorization server adds the
   parameters to the redirection URI query component using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224].

   For example, authenticates the resource owner and obtains an
   authorization server redirects decision (by asking the end-user's user-
   agent resource owner or by sending the following HTTP response:

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

   If the response type
   establishing approval via other means).

   When a decision is "token" or "code_and_token", established, the authorization server adds directs the parameters
   user-agent to the provided client redirection URI
   fragment component using the "application/x-www-form-urlencoded"
   format as defined by [W3C.REC-html401-19991224].

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

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

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

4.3.  Error user-
   agent.

4.2.2.  Access Token Response

   If the end-user denies resource owner grants the access request or if the request fails for
   reasons other than a missing or invalid redirection URI, request, the authorization
   server informs issues an access token and delivers it to the client by adding
   the following parameters to the fragment component of the redirection
   URI query component using the "application/x-www-form-urlencoded" format as defined format:

   access_token
         REQUIRED.  The access token issued by
   [W3C.REC-html401-19991224]:

   error the authorization server.
   token_type
         REQUIRED.  A single error code  The type of the token issued as described in
         Section 4.3.1.

   error_description 7.1.  Value is case insensitive.
   expires_in
         OPTIONAL.  A human-readable text providing
         additional information, used to assist  The duration in the understanding and
         resolution seconds of the error occurred.

   error_uri 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.
   scope
         OPTIONAL.  A URI identifying  The scope of the access request expressed as a human-readable web page
         with information about list
         of space-delimited strings.  The value is defined by the error, used to provide
         authorization server.  If the end-user
         with value contains multiple space-
         delimited strings, their order does not matter, and each string
         adds an additional information about access range to the error. requested scope.  The
         authorization server SHOULD include the parameter if the
         requested scope is different from the one requested by the
         client.

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

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

     HTTP/1.1 302 Found
     Location: https://client.example.com/cb?error=access_denied http://example.com/rd#access_token=FJQbwq9&
               token_type=example&expires_in=3600

   The client SHOULD ignore unrecognized response parameters.  The
   access token string size is left undefined by this specification.
   The client should avoid making assumptions about value sizes.  The
   authorization server should document the size of any value it issues.

4.2.2.1.  Error Response

   If the request fails due to a missing missing, invalid, or invalid mismatching
   redirection URI, the authorization server SHOULD inform the end-user resource
   owner of the error, and MUST NOT redirect the end-user's user-agent to the
   invalid redirection URI.

4.3.1.  Error Codes

   The

   If the resource owner denies the access request or if the request
   fails for reasons other than a missing or invalid redirection URI,
   the authorization server includes one of informs the client by adding the following error codes
   with
   parameters to the fragment component of the redirection URI using the
   "application/x-www-form-urlencoded" format:

   error response:
         REQUIRED.  A single error code from the following:
         invalid_request
               The request is missing a required parameter, includes an
               unsupported parameter or parameter value, or is otherwise
               malformed.
         invalid_client
               The client identifier provided is invalid.
         unauthorized_client
               The client is not authorized to use the requested response
         type.

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

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

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

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

   [[ Add mechanism for extending error codes ]]

5.  Obtaining an Access Token

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

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

   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.  The token endpoint URI MAY
   include a query component.

   The client authenticates with the authorization server by adding its
   client credentials authorized to the request as described in Section 3. an access token
               using this method.

         access_denied
               The resource owner or authorization server MAY allow unauthenticated access token requests
   when denied the client identity
               request.
         unsupported_response_type
               The authorization server does not matter (e.g. anonymous client) or
   when the client identity is established via other means (e.g. using support obtaining an assertion
               access grant).

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

   grant_type
         REQUIRED. this method.
         invalid_scope
               The access grant type included requested scope is invalid, unknown, or malformed.
   error_description
         OPTIONAL.  A human-readable text providing additional
         information, used to assist in the request.
         Value MUST be one understanding and resolution
         of "authorization_code", "password",
         "refresh_token", "client_credentials", or an absolute the error occurred.
   error_uri
         OPTIONAL.  A URI identifying an assertion format supported by a human-readable web page with
         information about the authorization
         server.

   scope
         OPTIONAL.  The scope of error, used to provide the access request expressed as a list
         of space-delimited strings.  The value of resource owner
         with additional information about the "scope" error.
   state
         REQUIRED if the "state" parameter
         is defined by was present in the client
         authorization server.  If request.  Set to the exact value contains
         multiple space-delimited strings, their order does not matter,
         and each string adds an additional access range to received from
         the
         requested scope.  If client.

   For example, the access grant being used already
         represents an approved scope (e.g. authorization code,
         assertion), server redirects the user-agent by
   sending the following HTTP response:

     HTTP/1.1 302 Found
     Location: https://client.example.com/cb#error=access_denied

4.3.  Resource Owner Password Credentials

   The resource owner password credentials flow is suitable in cases
   where the resource owner has a trust relationship with the client,
   such as its computer operating system or a highly privileged
   application.  The authorization server should take special care when
   enabling the requested scope MUST be equal or lesser than flow, and only when other flows are not viable.

   The flow is suitable for clients capable of obtaining the scope previously granted, resource
   owner credentials (username and if omitted password, typically using an
   interactive form).  It is treated also used to migrate existing clients using
   direct authentication schemes such as
         equal HTTP Basic or Digest
   authentication to OAuth by converting the previously approved scope.

   In addition, stored credentials with an
   access token.

   The method through which the client MUST include the appropriate parameters
   listed for obtains the selected access grant type as described in
   Section 5.1.

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

5.1.  Access Grant Types scope of this specification.  The client requests
   MUST discard the credentials once an access token using an authorization code,
   resource owner password credentials, client credentials, refresh
   token, or assertion.

5.1.1. has been obtained.

     +----------+
     | Resource |
     |  Owner   |
     |          |
     +----------+
          v
          |
         (A) Password Credentials
          |
          v
     +---------+                                  +---------------+
     |         |          Client Credentials      |               |
     |         |>--(B)---- & Resource Owner ----->|               |
     | Client  |         Password Credentials     | Authorization Code |
     |         |                                  |     Server    |
     |         |<--(C)---- Access Token ---------<|               |
     |         |    (w/ Optional Refresh Token)   |               |
     +---------+                                  +---------------+

            Figure 5: Resource Owner Password Credentials Flow

   The client flow illustrated in Figure 5 includes the authorization code using the
   "authorization_code" access grant type and the following parameters:

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

   redirect_uri
         REQUIRED. steps:

   (A)  The redirection URI used in the initial request.

   For example, resource owner provides the client makes with its username and
        password.
   (B)  The client requests an access token from the following HTTP request authorization
        server's token endpoint by including authenticating using its client
        credentials, and includes the credentials via received from 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
        resource owner.
   (C)  The authorization server MUST:

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

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

   If the request is valid, the authorization server issues a successful
   response as described in Section 5.2.

5.1.2.  Resource Owner Password Credentials an access
        token.

4.3.1.  Access Token Request

   The client includes makes a request to the token endpoint by adding the
   following parameter using the "application/x-www-form-urlencoded"
   format in the HTTP request entity-body:

   grant_type
         REQUIRED.  Value MUST be set to "password".
   username
         REQUIRED.  The resource owner credentials using username.

   password
         REQUIRED.  The resource owner password.
   scope
         OPTIONAL.  The scope of the
   "password" access grant type request expressed as a list
         of space-delimited strings.  The value 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 following parameters: requested scope.

   The client includes its authentication credentials as described in
   Section 2

   [[ add internationalization consideration for username and password
   ]]

   username
         REQUIRED.  The resource owner's username.

   password
         REQUIRED.  The resource owner's password.

   For example, the client makes the following HTTP request by including
   its client credentials via the "client_id" and "client_secret" parameter described in
   Section 3
   parameters, 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 MUST:

   o  Validate the client credentials (if
   present) and end-user credentials and if credentials.
   o  Validate the resource owner password credentials.

   If the request is valid issue and authorized, the authorization server
   issues an access token
   response and optional refresh token, and responds as
   described in Section 5.2.

5.1.3. 5.

4.4.  Client Credentials

   The client can request an access token using only its client
   credentials using the "client_credentials" access grant type.  When
   omitting an explicit access grant, when the client is requesting access to the protected
   resources under its control, or those of another resource owner which
   has been previously arranged with the authorization server (the
   method of which is beyond the scope of this specification).

5.1.4.  Refresh

     +---------+                                  +---------------+
     |         |                                  |               |
     |         |>--(A)--- Client Credentials ---->| Authorization |
     | Client  |                                  |     Server    |
     |         |<--(B)---- Access Token ---------<|               |
     |         |    (w/ Optional Refresh Token)   |               |
     +---------+                                  +---------------+

                     Figure 6: Client Credentials Flow

   The client flow illustrated in Figure 6 includes the refresh following steps:

   (A)  The client requests an access token from the token endpoint by
        authenticating using its client credentials.
   (B)  The authorization server validates the "refresh_token"
   access grant type client credentials and
        issues an access token.

4.4.1.  Access Token Request

   The client makes a request to the token endpoint by adding the
   following parameter:

   refresh_token parameter using the "application/x-www-form-urlencoded"
   format in the HTTP request entity-body:

   grant_type
         REQUIRED.  Value MUST be set to "client_credentials".
   scope
         OPTIONAL.  The refresh token associated with scope of the access token request expressed as a list
         of space-delimited strings.  The value 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 be refreshed. the requested scope.

   The client includes its authentication credentials as described in
   Section 2

   For example, the client makes the following HTTP request by including
   its client credentials via the "client_id" and "client_secret" parameter described in
   Section 3
   parameters, 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

     grant_type=client_credentials&client_id=s6BhdRkqt3&
     client_secret=47HDu8s

   The authorization server MUST verify validate the client credentials (if
   present), the validity of the refresh token, and that the resource
   owner's authorization is still valid. credentials.

   If the request is valid, the
   authorization server issues an access token response as described in
   Section 5.2.  The authorization server MAY issue a new refresh token,
   in which case, the client MUST discard valid and authorized, the old refresh authorization server
   issues an access token and
   replace it with the new optional refresh token.

5.1.5.  Assertion token, and responds as
   described in Section 5.

4.5.  Extensions

   The client includes uses an assertion extension grant type by specifying the assertion format grant type
   using an absolute URI (as defined (defined by the authorization server) as the
   value of the "grant_type" parameter of the token endpoint, and by
   adding the following
   parameter:

   assertion
         REQUIRED.  The assertion. any additional parameters necessary.

   For example, to request an access token using a SAML 2.0 assertion
   grant type, the client makes the following HTTP request using
   transport-layer security, and client authentication is achieved via
   the assertion 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=urn%3Aoasis%3Anames%3Atc%3ASAML%3A2.0%3Aassertion&
     assertion=PHNhbWxwOl[...omitted

     grant_type=http%3A%2F%2Foauth.net%2Fgrant_type%2Fassertion%2F
     saml%2F2.0%2Fbearer&assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ
     [...omitted for brevity...]ZT4%3D

   The authorization server MUST validate the client credentials (if
   present) brevity...]V0aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-

   Client authentication and the scope of the grant are obtained via the
   assertion and if as defined by [I-D.ietf-oauth-saml2-bearer].

5.  Issuing an Access Token

   If the access token request is valid and authorized, the
   authorization server issues an access token
   response and optional refresh
   token as described in Section 5.2.  The authorization server
   SHOULD NOT issue a refresh token (instead, it should require 5.1.  If the request failed client to use the same
   authentication or new assertion).

   Authorization servers SHOULD issue access tokens with a limited
   lifetime and require clients to refresh them by requesting a new
   access token using the same assertion if it is still valid.
   Otherwise invalid, the client MUST obtain a new valid assertion. authorization server return an
   error response as described in Section 5.2.  Access Token

5.1.  Successful Response

   After receiving and verifying a valid and authorized access token
   request from the client, the

   The authorization server issues the an 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 issued as described in
         Section 6.1. 7.1.  Value is case insensitive.
   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. generated.
   refresh_token
         OPTIONAL.  The refresh token which can be 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. as described
         in Section 6.
   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 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 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",
       "token_type":"example",
       "expires_in":3600,
       "refresh_token":"8xLOxBtZp8"
       "refresh_token":"8xLOxBtZp8",
       "example_parameter":"example-value"

     }

   Clients

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

5.3. it issues.

5.2.  Error Response

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

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

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

     {
       "error":"invalid_request"
     }

   If the client provided invalid credentials using an HTTP
   authentication scheme via the "Authorization" request header field,
   the authorization server MUST respond with the a HTTP 401 (Unauthorized)
   status code. code, and include the "WWW-Authenticate" response header field
   matching the authentication scheme used by the client.  Otherwise,
   the authorization server
   SHALL MUST respond with the HTTP 400 (Bad Request)
   status code.

5.3.1.  Error Codes

   The authorization server includes one of constructs the response by adding the
   following error codes
   with parameter to the error response:

   error
         REQUIRED.  A single error code from the following:
         invalid_request
               The request is missing a required parameter, includes an
               unsupported parameter or parameter value, repeats a
               parameter, includes multiple credentials, utilizes more
               than one mechanism for authenticating the client, or is
               otherwise malformed.
         invalid_client
         The client identifier provided is invalid, the client
               Client authentication failed to
         authenticate, the (e.g. unknown client, no
               client did not include its credentials,
         provided credentials included, multiple client credentials, credentials
               included, or used unsupported credentials type.

   unauthorized_client
         The authenticated client is not authorized to use the access
         grant type provided. type).
         invalid_grant
               The provided access authorization grant is invalid, expired,
               revoked, or revoked (e.g.
         invalid assertion, expired does not match the redirection URI used in
               the authorization token, bad end-user
         password credentials, or mismatching request.
         unauthorized_client
               The authenticated client is not authorized to use this
               authorization code and
         redirection URI). grant type.
         unsupported_grant_type
               The access authorization grant included - its type or another attribute - is not supported by the
               authorization server.

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

   [[ Add mechanism for extending
   error_description
         OPTIONAL.  A human-readable text providing additional
         information, used to assist in the understanding and resolution
         of the error codes ]]

6.  Accessing occurred.
   error_uri
         OPTIONAL.  A URI identifying a Protected Resource

   Clients access protected resources by presenting an access token human-readable web page with
         information about the error, used to provide the resource server. owner
         with additional information about the error.

   The resource server 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.

   For example:

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

     {
       "error":"invalid_request"
     }

6.  Refreshing an Access Token

   The client makes a request to the token endpoint by adding the
   following parameter using the "application/x-www-form-urlencoded"
   format in the HTTP request entity-body:

   grant_type
         REQUIRED.  Value MUST validate be set to "refresh_token".
   refresh_token
         REQUIRED.  The refresh token issued along the access token and ensure it has not expired and that its
         being refreshed.
   scope covers
         OPTIONAL.  The scope of the
   requested resource. access request expressed as a list
         of space-delimited strings.  The methods used value is defined by the resource server to
   validate
         authorization server.  If the value contains multiple space-
         delimited strings, their order does not matter, and each string
         adds an additional access token are beyond range to the requested scope.  The
         requested scope MUST be equal or lesser than the scope of this specification,
   but generally involve an interaction or coordination between
         originally granted by the resource server owner, and authorization server. if omitted is
         treated as equal to the previously approved scope.

   The method client includes its authentication credentials as described in which
   Section 2

   For example, the client utilized makes the access token to
   authenticate with following HTTP request by including
   its client credentials via the resource "client_id" and "client_secret"
   parameters, 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

   The authorization server depends on MUST validate the type of access
   token issued by client credentials, the
   refresh token, and verify that the resource owner's 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 is
   still valid.  If valid, the protected resource request does not include authentication
   credentials, contains authorization server issues an invalid access
   token response as described in Section 5.

   The authorization server MAY issue a new refresh token, or is malformed, in which
   case, the
   resource server client MUST include the HTTP "WWW-Authenticate" response
   header field.  The "WWW-Authenticate" header field uses discard the framework
   defined by [RFC2617] as follows:

     challenge       = "OAuth2" [ RWS 1#param ]

     param           = scope /
                       error / error-desc / error-uri /
                       ( token "=" ( old refresh token / quoted-string ) )

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

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

     error           = "error" "=" quoted-string
     error-desc      = "error_description" "=" quoted-string
     error-uri       = "error_uri" = <"> URI-reference <"> and replace it
   with the new refresh token.

7.  Accessing Protected Resources

   The "scope" attribute is a space-delimited list of scope values
   indicating client accesses protected resources by presenting the required scope of access
   token to the resource server.  The resource server MUST validate the
   access token for accessing and ensure it has not expired and that its scope covers
   the requested resource.  The "scope" attribute MUST NOT appear more than
   once.

   If methods used by the protected resource request included an server to
   validate the access token and failed
   authentication, are beyond the scope of this specification,
   but generally involve an interaction or coordination between the
   resource server SHOULD include and the "error"
   attribute to provide authorization server.

   The method in which the client with the reason why utilized the access
   request was declined.  The parameter value is described in
   Section 6.2.1.  In addition, token to
   authenticate with the resource server MAY include depends on the
   "error_description" attribute to provide a human-readable
   explanation, and type of access
   token issued by the authorization server.  Typically, it involves
   using the "error-uri" attribute HTTP "Authorization" request header field with an absolute URI
   identifying a human-readable web page explaining
   authentication scheme defined by the error. access token type specification.

7.1.  Access Token Types

   The
   "error", "error_description", and "error_uri" attribute MUST NOT
   appear more than once.

   For example, in response access token type provides the client with the information
   required to a protected resource request without
   authentication:

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: OAuth2

   And in response successfully utilize the access token to make a protected
   resource request (along with an
   authentication attempt using an expired access token:

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: OAuth2
                       error="invalid_token",
                       error_description="The access type-specific attributes).

   For example, the "bearer" token expired"

6.2.1.  Error Codes

   When a request fails, type defined in
   [I-D.ietf-oauth-v2-bearer] is utilized by simply including the resource server responds using access
   token string in the
   appropriate HTTP status code (typically, 400, 401, or 403), and
   includes one of request:

     GET /resource/1 HTTP/1.1
     Host: example.com
     Authorization: BEARER h480djs93hd8

   while the following error codes "mac" token type defined in the response:

   invalid_request
         The request [I-D.hammer-oauth-v2-mac-token]
   is missing utilized by issuing a required parameter, includes an
         unsupported parameter or parameter value, repeats the same
         parameter, uses more than one method for including an token secret together with the access
         token, or token
   which is otherwise malformed.  The resource server SHOULD
         respond with used to sign certain components of the HTTP 400 (Bad Request) status code.

   invalid_token
         The requests:

     GET /resource/1 HTTP/1.1
     Host: example.com
     Authorization: MAC token="h480djs93hd8",
                        timestamp="137131200",
                        nonce="dj83hs9s",
                        signature="kDZvddkndxvhGRXZhvuDjEWhGeE="

   Each access token provided is expired, revoked, malformed, or
         invalid for other reasons.  The resource SHOULD respond type definition specifies the additional attributes
   (if any) sent to the client together with the "access_token" response
   parameter.  It also defines the HTTP 401 (Unauthorized) status code.  The client MAY
         request a new authentication method used to
   include the access token and retry the when making a protected resource request.

   insufficient_scope
         The request requires higher privileges than provided by

8.  Extensibility

8.1.  Defining Access Token Types

   Access token types can be defined in one of two ways: registered in
   the access token.  The token type registry (following the procedures in
   Section 10.1), or use the "x_" type name prefix.

   Types utilizing the "x_" name prefix MUST be limited to vendor-
   specific implementations that are not commonly applicable, and are
   specific to the implementation details of the resource server SHOULD respond with where
   they are used.  If a vendor-specific type requires additional vendor-
   specific token response parameters, they MUST also use the HTTP
         403 (Forbidden) status code "x_" name
   prefix.

   All other types MUST be registered, and MAY include the "scope"
         attribute with MUST NOT use the scope necessary "x_" type
   name prefix.  Type names MUST conform to access the protected
         resource.

   [[ Add mechanism for extending error codes ]] type-name ABNF.  If the request lacks any authentication information (i.e. the client
   was unaware authentication is necessary or attempted using an
   unsupported
   type definition includes a new HTTP authentication method), the resource server SHOULD not
   include an error code or other error information.

   For example:

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: OAuth2

7.  Extensibility

7.1.  Defining New Client Credentials Types

   [[ TBD ]]

7.2. scheme, the type
   name SHOULD be identical to the authentication scheme name (as
   defined by [RFC2617]).

     type-name  = 1*name-char
     name-char   = "-" / "." / "_" / DIGIT / ALPHA

8.2.  Defining New Endpoint Parameters

   Applications that wish to define new

   New request or response parameters for use with the end-user authorization
   endpoint or the token endpoint SHALL do so can be added in one of two ways: register them
   registered in the parameters registry (following the procedures in
   Section 9.1), 10.2), 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 syntax of an existing parameter).

     param-name  = 1*name-char
     name-char   = "-" / "." / "_" / DIGIT / ALPHA

8.3.  Defining New Authorization Grant Types

   New authorization grant types can be defined by assigning them a
   unique URI for use with the "grant_type" parameter.  If the extension
   grant type requires additional token endpoint parameters, they MUST
   be registered in the OAuth parameters registry as described by
   Section 10.2.

9.  Security Considerations

   [[ TBD ]]

10.  IANA Considerations

10.1.  The OAuth Access Token Type Registry

   This specification establishes the OAuth access token type registry.

   Access token types 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 access toke type: 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 existing parameter).

     param-name  = 1*name-char
     name-char   = "-" / "." / "_" / DIGIT / ALPHA

7.3.  Defining New Header Field Parameters

   Applications explanation and, if applicable, suggestions as to how to make the
   request successful.  Registration requests that wish are undetermined for
   a period longer than 21 days can be brought to define new parameters the IESG's attention
   (using the iesg@iesg.org mailing list) for use in resolution.

10.1.1.  Registration Template

   Type name:
      The name requested (e.g., "example").
   Additional Token Endpoint Response Parameters:
      Additional response parameters returned together with the OAuth
   "WWW-Authenticate" header field
      "access_token" parameter.  New parameters MUST register them be separately
      registered in the OAuth parameters
   registry, following the procedures in registry as described by
      Section 9.1.

   Parameter names MUST conform to the param-name ABNF and MUST NOT
   begin with "x_".  Parameter values MUST conform 10.2.
   HTTP Authentication Scheme(s):
      The HTTP authentication scheme name(s), if any, used to the param-value
   ABNF and their syntax MUST be well-defined (e.g.,
      authenticate protected resources requests using ABNF, or a
   reference to access token of
      this type.
   Change controller:
      For standards-track RFCs, state "IETF".  For others, give the syntax name
      of an existing parameter).

     param-value  = quoted-value | quoted-string

7.4.  Defining New Access Grant Types

   The assertion access grant type allows the authorization server responsible party.  Other details (e.g., postal address,
      e-mail address, home page URI) may also be included.

   Specification document(s):
      Reference to
   accept additional access grants not specified.  Applications document that specifies the parameter, preferably
      including a URI that
   wish to define additional access grant types can do so by utilizing be used to retrieve a
   new or existing assertion type and format.

8.  Security Considerations

   [[ TBD ]]

9.  IANA Considerations

9.1. copy of the
      document.  An indication of the relevant sections may also be
      included, but is not required.

10.2.  The OAuth Parameters Registry

   This document specification establishes the OAuth parameters registry.

   Additional parameters to be use for inclusion in the end-user authorization endpoint
   request, the end-user authorization endpoint response, the token endpoint
   request, or the token endpoint response, 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.

9.1.1.

10.2.1.  Registration Template

   Parameter name:  The name requested (e.g., "example").
      The name requested (e.g., "example").
   Parameter usage location:
      The location(s) where parameter can be used.  The possible
      locations are: authorization request, authorization response,
      token request, or token response.
   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.

10.2.2.  Initial Registry Contents

   The OAuth Parameters Registry's initial contents are:

   o  Parameter name: client_id
   o  Parameter usage location: authorization request, token request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: client_secret
   o  Parameter usage location: token request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: response_type
   o  Parameter usage location: authorization request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: redirect_uri
   o  Parameter usage location: authorization request, token request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: scope
   o  Parameter usage location: authorization request, authorization
      response, token request, token response
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: state
   o  Parameter usage location: authorization request, authorization
      response
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: code
   o  Parameter usage location:  The location(s) where parameter can be
      used.  The possible locations are: the end-user authorization
      endpoint request, the end-user response, token request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]
   o  Parameter name: error_description
   o  Parameter usage location: authorization endpoint response,
      the token endpoint request, the response
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: error_uri
   o  Parameter usage location: authorization response, token endpoint response
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: grant_type
   o  Parameter usage location: token request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: access_token
   o  Parameter usage location: authorization response, the or
      the "WWW-Authenticate" header field. token response
   o  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. IETF
   o  Specification document(s):  Reference to [[ this 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.

9.1.2.  Example

   The following is the parameter registration ]]

   o  Parameter name: token_type
   o  Parameter usage location: authorization response, token response
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: expires_in
   o  Parameter usage location: authorization response, token response
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: username
   o  Parameter usage location: token request for the "scope"
   parameter as defined in
   o  Change controller: IETF
   o  Specification document(s): [[ this specification: document ]]

   o  Parameter name:  scope password
   o  Parameter usage location: token request
   o  Change controller: IETF
   o  Specification document(s): [[ this document ]]

   o  Parameter name: refresh_token
   o  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. response
   o  Change controller: IETF
   o  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, Phil
   Hunt, 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, Christian
   Stuebner, Paul Tarjan, Franklin 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 ]]

   -12

   o  Complete restructure with lots of new prose.
   o  Removed terminology and expanded terms in overview.
   o  Changed assertions to extensions and added informative reference
      to the SAML 2.0 extension.
   o  Renamed access grant to authorization grant.
   o  Clarified 'token_type' as case insensitive.
   o  Authorization endpoint requires TLS when an access token is
      issued.

   o  Removed client assertion credentials, mandatory HTTP Basic
      authentication support for client credentials, WWW-Authenticate
      header, and the OAuth2 authentication scheme.
   o  Changed implicit grant (aka user-agent flow) error response from
      query to fragment.
   o  Removed the 'redirect_uri_mismatch' error code since in such a
      case, the authorization server must not send the error back to the
      client.
   o  Added parameter registration for all parameters in this
      specification.
   o  Defined access token type registry.

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

10.

11.  References

10.1.

11.1.  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.

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

   [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., Raggett, D., 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>.

10.2.

11.2.  Informative References

   [I-D.hammer-oauth-v2-mac-token]
              Hammer-Lahav, E., "HTTP Authentication: MAC
              Authentication", draft-hammer-oauth-v2-mac-token-01 (work
              in progress), January 2011.

   [I-D.ietf-oauth-saml2-bearer]
              Campbell, B. and C. Mortimore, "SAML 2.0 Bearer Assertion
              Grant Type Profile for OAuth 2.0",
              draft-ietf-oauth-saml2-bearer-00 (work in progress),
              December 2010.

   [I-D.ietf-oauth-v2-bearer]
              Jones, M., Hardt, D., and D. Recordon, "The OAuth 2.0
              Protocol: Bearer Tokens", draft-ietf-oauth-v2-bearer-01
              (work in progress), December 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 dr@fb.com
   URI:   http://www.davidrecordon.com/
   Dick Hardt
   Microsoft

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