Network Working Group                               E. Hammer-Lahav, Ed.
Internet-Draft                                                    Yahoo!
Intended status: Standards Track                             D. Recordon
Expires: December 13, 17, 2010                                      Facebook
                                                                D. Hardt
                                                               Microsoft
                                                           June 11, 15, 2010

                         The OAuth 2.0 Protocol
                         draft-ietf-oauth-v2-07
                         draft-ietf-oauth-v2-08

Abstract

   This specification describes the OAuth 2.0 protocol.  OAuth provides
   a method for making authenticated HTTP requests using a token - an
   string used to denote an access grant with specific scope, duration,
   and other attributes.  Tokens are issued to third-party clients by an
   authorization server with the approval of the resource owner.  OAuth
   defines multiple flows for obtaining a token to support a wide range
   of client types and user experience.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on December 13, 17, 2010.

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4  3
     1.1.  Terminology  . . . . .  Notational Conventions . . . . . . . . . . . . . . . . . .  4  3
     1.2.  Overview . .  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6  4
     1.3.  Example  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  8  5
     1.4.  Notational Conventions  Client Profiles  . . . . . . . . . . . . . . . . . .  8
   2.  Client Flows . . .  8
       1.4.1.  Web Server . . . . . . . . . . . . . . . . . . . . . .  8
     2.1.  Web Server Flow
       1.4.2.  User-Agent . . . . . . . . . . . . . . . . . . . . .  8
     2.2.  User-Agent Flow .  9
       1.4.3.  Native Application . . . . . . . . . . . . . . . . . . 11
       1.4.4.  Autonomous . . 10
     2.3.  Username and Password Flow . . . . . . . . . . . . . . . . 11
     2.4. . . . . 12
   2.  Client Credentials Flow . . . . . . . . . . . . . . . . . 13
     2.5.  Assertion Flow . . . . . 12
     2.1.  Basic Client Credentials . . . . . . . . . . . . . . . . . 13
     2.6.  Native Application Considerations
   3.  Obtaining End-User Authorization . . . . . . . . . . . . 14
   3.  Client Credentials . . . 14
     3.1.  Authorization Server Response  . . . . . . . . . . . . . . 16
   4.  Obtaining an Access Token  . . . . . . 15
     3.1.  Client Authentication . . . . . . . . . . . . 17
     4.1.  Access Grant Parameters  . . . . . . 15
   4.  Establishing Resource Owner Authorization . . . . . . . . . . 16
     4.1.  Verification . 18
       4.1.1.  Authorization Code . . . . . . . . . . . . . . . . . . 18
       4.1.2.  Resource Owner Basic Credentials . . 17
       4.1.1.  End-User Authorization Endpoint . . . . . . . . . 19
       4.1.3.  Assertion  . . 17
     4.2.  Resource Owner Credentials . . . . . . . . . . . . . . . . 20
     4.3.  Assertion . . . . 20
       4.1.4.  Refresh Token  . . . . . . . . . . . . . . . . . . . . 21
   5.  Obtaining an 20
     4.2.  Access Token Response  . . . . . . . . . . . . . . . . . . 21
     5.1.  Token Endpoint . .
     4.3.  Error Response . . . . . . . . . . . . . . . . . . . . 21
       5.1.1.  Verification Code . . 22
       4.3.1.  Error Codes  . . . . . . . . . . . . . . . . 22
       5.1.2.  Resource Owner Credentials . . . . . 23
   5.  Accessing a Protected Resource . . . . . . . . . 22
       5.1.3.  Assertion . . . . . . . 23
     5.1.  The Authorization Request Header Field . . . . . . . . . . 24
     5.2.  URI Query Parameter  . . . . . 23
       5.1.4.  Refresh Token . . . . . . . . . . . . . . 25
     5.3.  Form-Encoded Body Parameter  . . . . . . 24
       5.1.5.  Access Token Response . . . . . . . . . 25
   6.  The WWW-Authenticate Response Header Field . . . . . . . 25
       5.1.6.  Error Response . . . 26
   7.  Security Considerations  . . . . . . . . . . . . . . . . . 26
   6.  Accessing a Protected Resource . . 27
   8.  IANA Considerations  . . . . . . . . . . . . . . 27
     6.1.  The Authorization Request Header . . . . . . . . . . . . . 28
     6.2.  URI Query Parameter  . . . . . . . . . . . . . . . . . . . 28
     6.3.  Form-Encoded Body Parameter  . . . . . . . . . . . . . . . 29
   7.  Identifying a Protected Resource . . . . . . . . . . . . . . . 30
     7.1.  The WWW-Authenticate Response Header . . . . . . . . . . . 30
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Examples  . 31
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 27
   Appendix A. B.  Contributors  . . . . . . . . . . . . . . . . . . . . 31 27
   Appendix B. C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 31 28
   Appendix C. D.  Document History  . . . . . . . . . . . . . . . . . . 32
   10. 28
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     10.1. 31
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 34
     10.2. 31
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 35 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36 32

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, a client accessing a protected resource on a
   server presents the resource owner's credentials in order to
   authenticate and gain access.

   Resource owners should not be required

   OAuth introduces a third role to share their credentials
   when granting third-party applications the traditional client-server
   authentication model: the resource owner.  In OAuth, the client
   (which is usually not the resource owner, but is acting on its
   behalf) requests access to resources controlled by the resource owner
   and hosted by the resource server.

   In addition to removing the need for resource owners to share their protected
   resources.  They
   credentials, resource owners should also have the ability to restrict
   access to a limited subset of the resources they control, to limit
   access duration, or to limit access to the HTTP methods supported by these
   resources.

   OAuth provides a method for making authenticated HTTP requests

   Instead of using
   a token - an identifier used the resource owner's credentials to denote access protected
   resources, clients obtain an access grant with token (which denotes a specific
   scope, duration, and other attributes. attributes).  Tokens are issued to third-
   party clients client by an authorization server with the approval of the
   resource owner.  Instead of sharing their credentials with the
   client, resource owners grant access by authenticating directly with
   the authorization server which in turn issues a token to the client.  The client uses the access token to authenticate with access the resource server
   and gain access.
   protected resources.

   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
   the photo sharing service (authorization server) which issues the
   printing service delegation-specific credentials (token).

   This specification defines the use of OAuth over HTTP [RFC2616] (or
   HTTP over TLS as defined by [RFC2818]).  Other specifications may
   extend it for use with other transport protocols.

1.1.  Terminology

   resource server
         An HTTP [RFC2616] server capable  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 accepting authenticated
         resource requests using

   [I-D.ietf-httpbis-p1-messaging].  Additionally, the OAuth protocol. realm and auth-
   param rules are included from [RFC2617].

   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 from a
         resource server using an
         OAuth-authenticated request.

   client
         An HTTP client

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

   client
         An application obtaining authorization and making authenticated requests for protected resources using the OAuth protocol.
         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 grant authorization issued to the
         client.  The string is usually opaque to the client and can
         self-contain the authorization information in a verifiable
         manner (i.e. signed), or denotes an identifier used to retrieve
         the
         authorization information.

   access token
         A token used by the client to make authenticated requests on
         behalf of the resource owner.  Access tokens  Tokens represent a specific scope, duration,
         and other access authorization attributes granted by the resource
         owner and enforced by the resource server and authorization
         servers.

   refresh

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

         refresh token
         with
               A token used by the client to obtain a new access token
               (in addition or as a replacement for an expired access
               token), without having to involve the resource owner.

         authorization code  A refresh token is used when the access short-lived token is valid
         for a shorter time period than the duration of representing the access
               grant
         granted provided by the resource owner. end-user.  The authorization code
               is used to obtain an access token and a refresh token.

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

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

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

   client identifier
         An unique identifier issued to the client to identify itself to
         the authorization server.  Client identifiers may have a
         matching secret.

1.2.  The client identifier is described in
         Section 2.

1.3.  Overview

   Clients interact with

   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 by requesting
   access (which is granted in obtain authorization from the form of resource owner,
   then exchange that access grant for an access token) from token (representing the
   authorization server,
   grant's scope, duration, and then by authenticating with other attributes).  The client accesses
   the protected resource
   server by presenting the access token.  Figure 1 demonstrates the
   flow between the client and authorization server (A, B), and the flow
   between the client and resource server (C, D), when the client is
   acting autonomously (the client is also token to the resource owner).
   server.

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

                     Figure 1: Generic Client-Server Abstract Protocol Flow

   Access token strings can use any internal structure agreed upon
   between

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

   (A)  The client requests authorization server and from the resource server, but their
   structure is opaque to the client.  Since owner.  The
        client should not interact directly with the access token provides resource owner
        (since that would exposing the client access resource owner's credentials to
        the protected resource for client), but instead requests authorization via an
        authorization server or other entities.  For example, the life of client
        directs the
   access token (or until revoked), resource owner to the authorization server should
   issue access tokens which expire within in
        turn issues it an appropriate time, usually
   much shorter than the duration of the access grant.  When an access token expires, cannot be avoided, the
        client can request a new access
   token from interacts directly with the authorization server by presenting its credentials
   again (Figure 1), or by using end-user, asking for the refresh token (if issued with the
   access token) as shown in Figure 2.  Once an expired access token has
   been replaced with a new access token (A, B), the client uses the new
   access token as before (C, D).

     +--------+                                  +---------------+
     |        |--(A)------ Refresh Token ------->| Authorization |
     |        |                                  |    Server     |
     |        |<-(B)------ Access Token ---------|               |
     |        |                                  +---------------+
     | Client |
     |        |            HTTP Request          +---------------+
     |        |--(C)--- with Access Token ------>|    Resource   |
     |        |                                  |     Server    |
     |        |<-(D)----- HTTP Response ---------|               |
     +--------+                                  +---------------+

                   Figure 2: Refreshing an Access Token

   This specification defines a number of authorization flows to support
   different client types and scenarios.  These authorization flows can
   be separated into three groups: user delegation flows, direct
   credentials flows, and autonomous flows.

   Additional authorization flows may be defined by other specifications
   to cover different scenarios and client types.

   User delegation flows are used to grant client access to protected
   resources by the end-user without sharing the end-user credentials
   (e.g. a username and password) with the client.  Instead, the end-
   user authenticates directly with the authorization server, and grants
   client access to its protected resources.  The user delegation flows
   defined by this specifications are:

   o  Web Server Flow - This flow is optimized for clients that are part
      of a web server application, accessible via HTTP requests.  This
      flow is described in Section 2.1.

   o  User-Agent Flow - This flow is designed for clients running inside
      a user-agent (typically a web browser).  This flow is described in
      Section 2.2.

   Direct credentials flows enable clients to obtain an access token
   with a single request using the client credentials or end-user
   credentials without seeking additional resource owner authorization.
   The direct credentials flows defined by this specification are:

   o  Username and Password Flow - This flow is used in cases where the
      end-user trusts the client to handle its credentials but it is
      still undesirable for the client to store the end-user's username
      and password.  This flow is only suitable when there is a high
      degree of trust between the end-user and the client.  This flow is
      described in Section 2.3.

   o  Client Credentials Flow - The client uses its credentials to
      obtain an access token.  This flow is described in Section 2.4.

   Autonomous flows enable clients to utilize existing trust
   relationships or different authorization constructs to obtain an
   access token.  They provide a bridge between OAuth and other trust
   frameworks.  The autonomous authorization flow defined by this
   specifications is:

   o  Assertion Flow - The client presents an assertion such as a SAML
      [OASIS.saml-core-2.0-os] assertion to the authorization server in
      exchange for an access token.  This flow is described in
      Section 2.5.

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

1.3.  Example

   [[ Todo ]]

1.4.  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 realm and auth-
   param rules are included from [RFC2617].

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

2.  Client Flows

2.1.  Web Server Flow

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

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

                         Figure 3: Web Server Flow

   The web server flow illustrated in Figure 3 includes the following
   steps:

   (A)  The web client initiates the flow by redirecting the end-user's
        user-agent to the end-user authorization endpoint as described
        in Section 4.1.1 using client type "web_server".  The client
        includes its client identifier, requested scope, local state,
        and a redirect URI to which the authorization server will send
        the end-user back once authorization is granted (or denied).

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

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

   (D)  The client requests an access token from the authorization
        server by authenticating and including the verification code
        received in the previous step as described in Section 5.1.

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

2.2.  User-Agent Flow

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

   Unlike other flows in which the client makes separate authorization end-
        user's username and access token requests, the client received the access token as a
   result of the authorization request in the form of an HTTP
   redirection. password.

   (B)  The client requests the authorization server to
   redirect the user-agent to another web server or local resource
   accessible to the browser which is capable of extracting the issued an access
   token from the response and passing it to the client.

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

          +----------+          Client Identifier     +----------------+
          |          |>---(A)-- & Redirection URI --->|                |
          |          |                                |                |
   End <--+  -  -  - +----(B)-- User authenticates -->|  Authorization |
   User   |          |                                |     Server     |
          |          |<---(C)-- Redirect URI --------<|                |
          |  Client  |       with Access Token        |                |
          |    in    |   (w/ Optional Refresh Token)  +----------------+
          |  Browser |            in Fragment
          |          |                                +----------------+
          |          |>---(D)-- Redirect URI -------->|                |
          |          |        without Fragment        |   Web Server   |
          |          |                                |   with Client  |
          |    (F)   |<---(E)-- Web Page with -------<|    Resource    |
          |  Access  |             Script             |                |
          |   Token  |                                +----------------+
          +----------+
                         Figure 4: User-Agent Flow

   The user-agent flow illustrated in Figure 4 includes
        authorization provided by the following
   steps:

   (A) resource owner.  The client sends the user-agent access grant
        can be expressed as:

        *  Authorization code - an access grant obtained via an
           authorization server.  The process used to the end-user obtain an
           authorization
        endpoint as code is described in Section 4.1.1 3.

        *  Assertion - an access grant obtained from entities using a
           different trust framework.  Assertions enable the client type
        "user-agent". to
           utilize existing trust relationships to obtain an access
           token.  They provide a bridge between OAuth and other trust
           frameworks.  The client includes access grant represented by an assertion
           depends on the assertion type, its client identifier,
        requested scope, local state, content, and a redirect URI to how it was
           issued, which are beyond the
        authorization server will send the scope of this specification.

        *  Basic end-user back once
        authorization credentials - obtained when interacting
           directly with an end-user.  Resource owner credentials should
           only be used when there is granted (or denied).

   (B)  The authorization server authenticates the end-user (via a high degree of trust between the
        user-agent) and establishes whether
           resource owner the end-user grants client (e.g. its computer operating system
           or
        denies a highly privileged application).  However, unlike the client's
           HTTP Basic authentication scheme defined in [RFC2617], the
           end-user's credentials are used in a single request and are
           exchanged for an access request. token and refresh token which
           eliminates the client need to store them for future use.

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

   (D)  The authorization server
        redirects validated the user-agent to the redirection URI provided
        earlier.  The redirection URI includes client credentials and
        the access grant, and issues an access token (and with an optional verification code) in the URI fragment.

   (D)  The user-agent follows
        refresh token.  Access token usually have a shorter lifetime
        than the redirection instructions by making an
        HTTP "GET" request access grant.  Refresh tokens usually have a lifetime
        equal to the web server which does not include duration of the
        fragment.  The user-agent retains access grant.  When an access token
        expires, the fragment information
        locally.  The user-agent MUST NOT include refresh token is used to obtain a new access token
        without having to request another access grant from the fragment component
        with resource
        owner (in which case, the request. refresh token acts as an access
        grant).

   (E)  The web server returns client makes a web page (typically an HTML page with
        an embedded script) capable of accessing the full redirection
        URI including the fragment retained by protect resource request to the user-agent, resource
        server, and
        extracting presents the access token (and other parameters) contained in
        the fragment. order to gain access.
        Accessing a protected resource is described in Section 5.

   (F)  The user-agent executes the script provided by the web resource server
        which extracts validates the access token token, and passes it to if valid,
        serves the client.  If
        a verification code was issued, request.

   When the client can pass it to a web
        server component to obtain another access token for additional
        server-based protected resources interaction.

2.3.  Username and Password Flow

   The username and password flow is suitable for clients capable acting on behalf of
   asking end-users for their usernames and passwords.  It itself (the client is also used
   to migrate existing clients using direct authentication schemes such
   as HTTP Basic or Digest authentication to OAuth by converting the
   end-user credentials stored with tokens.

   However, unlike
   resource owner), the client skips steps (A) and (B), and does not
   include an access grant in step (C).  When the client uses the HTTP Basic authentication scheme defined user-
   agent profile (described in

   [RFC2617], Section 1.4.2), the end-user's credentials are used in a single authorization request
   and are exchanged for
   (A) results in an access token (D), skipping steps (B) and refresh token which
   eliminates the client need to store them for future use. (C).

   The methods through which the client prompts end users for their
   usernames sizes of tokens and passwords is beyond other values received from the scope of authorization
   server, are left undefined by this specification.
   The client MUST discard  Clients should
   avoid making assumptions about value sizes.  Servers should document
   the usernames expected size of any value they issue.

1.4.  Client Profiles

   OAuth supports a wide range of client types by providing a rich and passwords once
   extensible framework for establishing authorization and exchaning it
   for an access
   token has been obtained.

   This flow token.  The methods detailed in this specification were
   designed to accomodate four client types: web servers, user-agents,
   native applications, and autonomous clients.  Additional
   authorization flows and client profiles may be defined by other
   specifications to cover additional scenarios and client types.

1.4.1.  Web Server

   The web server profile is suitable in cases where for clients capable of interacting
   with the end-user already has end-user's user-agent (typically a trust
   relationship with web browser) and capable
   of receiving incoming requests from the client, such authorization server (capable
   of acting as its computer operating system
   or highly privileged applications.  Authorization servers should take
   special care when enabling the username and password flow, and only
   when other delegation flows are not viable. an HTTP server).

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

                         Figure 5: Username and Password 2: Web Server Flow

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

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

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

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

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

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

1.4.2.  User-Agent

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

   Unlike other profiles in which the client with its username makes a separate end-user
   authorization request and password.

   (B)  The client requests an access token from requests, the authorization
        server by authenticating and including client
   receives the end-user's username
        and password, and desired scope access token as described a result of the end-user authorization
   request in Section 5.1.

   (C) the form of an HTTP redirection.  The client requests the
   authorization server validates to redirect the end-user credentials and user-agent to another web server
   or local resource accessible to the user-agent which is capable of
   extracting the client credentials and issues an access token.

2.4.  Client Credentials Flow

   The token from the response and passing it to the
   client.

   This user-agent profile does not utilize the client credentials flow is used when secret since the
   client acts executables reside on behalf of
   itself (the client is the resource owner), end-user's computer or when device which
   makes the client
   credentials are used to obtain an secret accessible and exploitable.  Because the
   access token representing a
   previously established access authorization.  The client secret is
   assumed to be high-entropy since encoded into the redirection URI, it is not designed to may be memorized
   by an end-user.

     +--------+                                  +---------------+ exposed
   to the end-user and other applications residing on the computer or
   device.

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

                         Figure 6: Client Credentials 3: User-Agent Flow

   The client credential user-agent flow illustrated in Figure 6 3 includes the following
   steps:

   (A)  The client requests an access token from sends the authorization
        server by authenticating and including user-agent to the desired scope end-user authorization
        endpoint as described in Section 5.1.  No additional 3 using client type
        "user-agent".  The client includes its client identifier,
        requested scope, local state, and a redirect URI to which the
        authorization server will send the end-user back once
        authorization grant
        information is needed. granted (or denied).

   (B)  The authorization server validates authenticates the client credentials and
        issues an access token.

2.5.  Assertion Flow

   The assertion flow is used when a client wishes to exchange an
   existing security token or assertion for an access token.  This flow
   is suitable when end-user (via the client is
        user-agent) and establishes whether the resource owner end-user grants or is acting on
   behalf of
        denies the resource owner (based on client's access request.

   (C)  If the content of end-user granted access, the assertion
   used).

   The assertion flow requires authorization server
        redirects the client to obtain a assertion (such as
   a SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
   or to self-issue an assertion prior user-agent to initiating the flow. redirection URI provided
        earlier.  The
   assertion format, the process by which redirection URI includes the assertion is obtained, and access token (and an
        optional authorization code) in the method of validating URI fragment.

   (D)  The user-agent follows the assertion are defined redirection instructions by the assertion
   issuer and the authorization server, and are beyond the scope of this
   specification.

     +--------+                                  +---------------+
     |        |                                  |               |
     |        |>--(A)------ Assertion ---------->| Authorization |
     | Client |                                  |     Server    |
     |        |<--(B)---- Access Token ---------<|               |
     |        |                                  |               |
     +--------+                                  +---------------+

                         Figure 7: Assertion Flow making a
        request to the web server which does not include the fragment.
        The assertion flow illustrated in Figure 7 includes user-agent retains the following
   steps:

   (A) fragment information locally.

   (E)  The client requests web server returns a web page (typically an access token from HTML page with
        an embedded script) capable of accessing the authorization
        server by authenticating and full redirection
        URI including the assertion, assertion
        type, fragment retained by the user-agent, and desired scope as described
        extracting the access token (and other parameters) contained in Section 5.1.

   (B)
        the fragment.

   (F)  The authorization user-agent executes the script provided by the web server validates
        which extracts the assertion access token and issues passes it to the client.  If
        an authorization code was issued, the client can pass it to a
        web server component to obtain another access token.

2.6. token for
        additional server-based protected resources interaction.

1.4.3.  Native Application Considerations

   Native application are clients running as native code on the end-
   user's computer or device (i.e. executing outside a browser user-agent or as
   a desktop program).  These clients are often capable of interacting
   with (or embedding) the end-user's user-agent but are incapable of
   receiving callback requests from the server (incapable of acting as
   an HTTP server).

   Native application clients can utilize many of the flows defined be implemented in
   this specification with little or no changes.  For example: different ways based
   on their requirements and desired end-user experience.  Native
   application clients can:

   o  Launch  Utilize the end-user authorization endpoint as described in
      Section 3 by launching an external user-agent and have it redirect back to the user-agent.  The client using can
      capture the response by providing a redirection URI with a custom
      URI scheme.  This works scheme (registered with the web server
      flow and user-agent flow.

   o  Launch an external user-agent and poll for changes operating system to invoke the window
      title.  This works with the web server flow with
      client application), or by providing a redirection URI pointing to
      a server-hosted
      custom redirect result page that resource under the client's control which puts the verification code
      response in the user-agent window title (from which the client can
      obtain the response by polling the user-agnet window, looking for
      a window title change).

   o  Utilize the end-user authorization endpoint as described in the
      title.

   o  Use
      Section 3 by using an embedded user-agent and obtain user-agent.  The client obtains the redirection URI.  This
      works
      response by directly communicating with the web server flow and user-agent flow. embedded user-agent.

   o  Use the username and password flow and prompt the  Prompt end-users for their credentials. basic credentials (username and
      password) and use them directly to obtain an access token.  This
      is generally discouraged as it hands the end-user's password
      directly to the 3rd party and may not work
      with some authentication schemes. is limited to basic credentials.

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

   o  External user-agents may improve completion rate as following:

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

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

   o  Embedded user-agents are less secure because users are
      authenticating in unidentified window without access to the
      protections offered by many user-agents.

1.4.4.  Autonomous

   Autonomous clients act on their own behalf (the client is also the
   resource owner), or utilize existing trust relationship or framework
   to establish authorization without directly involving the resource
   owner.

   Autonomous clients can be implemented in different ways based on
   their requirements and the existing trust framework they rely upon.
   Autonomous clients can:

   o  Obtain an access token by authenticating with the authorization
      server using their client credentials.  The scope of the access
      token is limited to the protected resources under the control of
      the client.

   o  Use an existing access grant expressed as an assertion using an
      assertion format supported by the authorization server.  Using
      assertions requires the client to obtain a assertion (such as a
      SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
      or to self-issue an assertion.  The assertion format, the process
      by which the assertion is obtained, and the method of validating
      the end-user
      may already be logged-in assertion are defined by the assertion issuer and not have to re-authenticate.

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

   o  Embedded user-agents are less secure because users are
      authenticating in unidentified window without access to beyond the
      protections offered by many user-agents.

3. scope of this
      specification.

2.  Client Credentials

   When requesting access from interacting with the authorization server, the client identifies
   itself using a set of client credentials.  The client credentials
   include a client identifier and an OPTIONAL symmetric
   shared secret. MAY include a secret or other means
   for the authorization server to authenticate the client.

   The means through which the client obtains these its credentials are beyond
   the scope of this specification, but usually involve registration
   with the authorization server.

   The client identifier is used by the authorization server to
   establish the identity [[ OAuth Discovery provides one way of the
   obtaining basic client for the purpose of presenting
   information to the resource owner prior to granting access, as well
   as for providing different service levels to different clients.  They
   can also be used to block unauthorized clients from requesting
   access. credentials ]]

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

3.1.  Client Authentication

   The token endpoint requires

   This specification provides one mean of authenticating the client to
   using a set of basic client credentials.  The authorization server
   MAY authenticate itself to the
   authorization server.  This is done client using any desired authentication scheme.

2.1.  Basic Client Credentials

   The basic client credentials include a client identifier and an
   OPTIONAL matching shared symmetric secret.  The client identifier and
   secret are included in the request using the HTTP Basic
   authentication scheme as defined in [RFC2617] by including the client
   identifier (and optional secret) in as the username and secret as the password.

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

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

     type=web_server&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

   Alternatively, the request.  The client
   identifier and secret are included in MAY include the request credentials using two the
   following request parameters: "client_id" and "client_secret".

   client_id
         REQUIRED.  The client identifier.

   client_secret  REQUIRED if the client identifier has a matching
         secret.

   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

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

   The client MAY include the client credentials using an other HTTP
   authentication scheme schemes which supports support authenticating using a username
   and password, instead of using the "client_id" and "client_secret"
   request parameters.  Including the client credentials using an HTTP
   authentication scheme fulfills the requirements of including the
   parameters as defined by the various flows. password.  The client MUST NOT include the client credentials
   using more than one mechanism.  If more than one mechanism is used,
   regardless if whether the credentials are identical, identical or valid, the server
   MUST reply with an HTTP 400 status code (Bad Request) and include the "multiple-credentials"
   "multiple_credentials" error message. code.

   The authorization server MUST accept the client credentials using
   both the request parameters, and the HTTP Basic authentication scheme
   as defined in [RFC2617].
   scheme.  The authorization server MAY support additional HTTP
   authentication schemes.

   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

     type=web_server&code=i1WsRn1uB1&
     redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

4.  Establishing Resource Owner

3.  Obtaining End-User Authorization

   Before

   When the client can obtain interacts with an access token, it must first attain
   authorization from end-user, the resource owner.  The methods through which end-user MUST first
   grant the client attains authorization are codified in the various authorization flows defined in Section 5, and depends on the client
   type and to access its trust relationship with protected resources.
   Once obtained, the resource owner.

   Resource owner authorization can be end-user access grant is expressed in multiple ways: a
   verification code obtained through direct interaction with as an end-
   user, the resource owner credentials (or the client credentials when
   authorization code which the client is also the resource owner) obtained through a trust
   relationship with the resource owner, or uses to obtain an assertion obtained
   through means beyond the scope of this specification.

4.1.  Verification Code

   When access token.
   To obtain an end-user is involved, the client attains authorization in the
   form of a verification code by sending the end-user to the
   authorization server to review and grant authorization, the request.  The client sends the end-user by directing the end-user's user-agent to
   the
   authorization server's end-user authorization endpoint.

4.1.1.  End-User Authorization Endpoint

   When directed to

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

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

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

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

   type
         REQUIRED.  The client type (user-agent or web server).
         Determines how the authorization server delivers the
         authorization response back to the client.  The parameter value
         MUST be set to "web_server" or "user_agent".

   client_id
         REQUIRED.  The client identifier as described in Section 3. 2.

   redirect_uri
         REQUIRED, unless a redirection URI has been established between
         the client and authorization server via other means.  An
         absolute URI to which the authorization server will redirect
         the user-agent to when the end-user authorization step is
         completed.  The authorization server SHOULD require the client
         to pre-register their redirection URI.  Authorization servers
         MAY restrict the redirection URI to not include a query
         component as defined by [RFC3986] section 3.

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

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

   The client directs the end-user to the constructed URI using an HTTP
   redirection response, or by other means available to it via the end-
   user's user-agent.  The request MUST use the HTTP "GET" method.

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

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

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

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

4.1.1.1.

3.1.  Authorization Server Response

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

   code
         REQUIRED if the client type is "web_server", otherwise
         OPTIONAL.  The verification authorization code generated by the
         authorization server.  The verification authorization code SHOULD expire
         shortly after it is issued and allowed for a single use.  The verification
         authorization code is bound to the client identifier and
         redirection URI.

   access_token
         REQUIRED if the client type is "user_agent", otherwise MUST NOT
         be included.  The access token.

   expires_in
         OPTIONAL.  The duration in seconds of the access token lifetime
         if an access token is included.

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

   If the end-user denies the access request, the authorization server
   informs the client by adding the following parameters to the
   redirection URI:

   error
         REQUIRED.  The parameter value MUST be set to "user_denied".

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

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

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

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

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

   If the client type is "user_agent", the authorization server adds the
   parameters to the redirection URI fragment component using the
   "application/x-www-form-urlencoded" format as defined by
   [W3C.REC-html401-19991224]. [[ replace form-encoded with JSON? ]]

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

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

4.2.  Resource Owner Credentials

   While OAuth seeks to eliminate the need for resource owners to share
   their credentials with the client, possesion of the resource owner
   credentials constitute an authorization grant (if supported by the
   authorization server).  Resource owner credentials should only be
   used when there is a high degree of trust between the resource owner
   the client.

   In cases where the client is also the resource owner, the client
   credentials can be used to obtain an access token provisioned for
   accessing the client's protected resources.

4.3.  Assertion

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

5.

4.  Obtaining an Access Token

   The client obtains an access token by authenticating with the
   authorization server and presenting its authorization grant.

   In many cases it is desirable to issue access tokens with a shorter
   lifetime than the duration of the authorization grant.  However, it
   may be undesirable to require the resource owner to authorize the
   request again.  Instead, the authorization server issues a refresh
   token in addition to the access token.  When the access token
   expires, the client can request a new access token without involving
   the resource owner as long as the authorization grant is still valid.
   The token refresh method is described in Section 5.1.4.

5.1.  Token Endpoint token by authenticating with the
   authorization server and presenting its access grant.

   After obtaining authorization from the resource owner, clients
   request an access token from the authorization server's token
   endpoint.  When requesting an access token, the client authenticates
   with the authorization server and includes the authorization access grant (in the
   form of a verification an authorization code, resource owner credentials, an
   assertion, or a refresh token).

   The location of the token endpoint can be found in the service
   documentation, or can be obtained by using [[ OAuth Discovery ]].
   The token endpoint URI MAY include a query component, which must be
   retained when adding additional query parameters.

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

   The client obtains requests an access token by constructing a token request
   and making an HTTP "POST" request.  The client constructs the request
   URI by:

   o  Adding by adding its client credentials to the request as described in
   Section 3.1.  For example, if the client uses a set of basic
      client credentials, it adds the "client_id" 2, and "client_secret" includes the following parameters to using the request (or uses
   "application/x-www-form-urlencoded" format in the HTTP Basic authentication
      scheme).

   o  Adding the authorization request
   entity-body:

   grant_type
         REQUIRED.  The access grand type included in the form request.
         Value MUST be one of a verification code,
      resource owner credentials, an assertion, "authorization_code",
         "user_basic_credentials", "assertion", "refresh_token", or refresh token.  If
         "none" (which indicates the client is acting on behalf of itself (the client is also
         itself).

   scope
         OPTIONAL.  The scope of the
      resource owner), no additional information is needed. access request expressed as a list
         of space-delimited strings.  The
      authorization grant value of the "scope" parameter
         is added 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 request URI query component
      using
         requested scope.  If the "application/x-www-form-urlencoded" format access grant being used already
         represents an approved scope (e.g. authorization code,
         assertion), the requested scope MUST be equal or lesser than
         the scope previously granted.

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

5.1.1.  Verification in
   Section 4.1.

4.1.  Access Grant Parameters

4.1.1.  Authorization Code

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

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

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

   For example, the client makes the following HTTPS request (line
   breaks are for display purposes only):

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

     client_id=s6BhdRkqt3&

     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 verify that the verification authorization code,
   client identity, client secret, and redirection URI are all valid and
   match its stored association.  If the request is valid, the
   authorization server issues a successful response as described in
   Section 5.1.5.

5.1.2. 4.2.

4.1.2.  Resource Owner Basic Credentials

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

   username
         REQUIRED.  The end-user's username.

   password
         REQUIRED.  The end-user's password.

   scope
         OPTIONAL.  The scope of the access request expressed as a list
         of space-delimited strings.  The value of the "scope" parameter
         is defined by the authorization server.  If using the value contains
         multiple space-delimited strings, their order does not matter,
   following parameters: [[ add internationalization consideration for
   username and each string adds an additional access range to the
         requested scope. password ]]

   username
         REQUIRED.  The end-user's username.

   password
         REQUIRED.  The end-user's password.

   For example, the client makes the following HTTPS request (line
   breaks are for display purposes only):

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

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

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

   The authorization server MUST validate the client credentials and
   end-user credentials and if valid issues an access token response as
   described in Section 5.1.5.

   If the client is acting on behalf of itself (the client is also the
   resource owner), the client authentication alone suffice and the
   "username" and "password" parameters MUST NOT be used.

5.1.3. 4.2.

4.1.3.  Assertion

   The client includes the assertion using the following parameters:

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

   assertion
         REQUIRED.  The assertion.

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

   For example, the client makes the following HTTPS request (line
   breaks are for display purposes only):

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

     client_id=s6BhdRkqt3&client_secret=diejdsks&

     grant_type=assertion&client_id=s6BhdRkqt3&client_secret=diejdsks&
     assertion_type=urn%3Aoasis%3Anames%sAtc%3ASAML%3A2.0%3Aassertion&
     assertion=PHNhbWxwOl...[ommited for brevity]...ZT4%3D

   The authorization server MUST validate the assertion and if valid
   issues an access token response as described in Section 5.1.5. 4.2.  The
   authorization server SHOULD NOT issue a refresh token.

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

5.1.4.

4.1.4.  Refresh Token

   Token refresh is used when the lifetime of an access token is shorter
   than the lifetime of the authorization grant.  It enables the client
   to obtain a new access token without having to go through the
   authorization flow again or involve the resource owner.

   The client includes the refresh token using the following parameters:

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

   For example, the client makes the following HTTPS request (line break
   are for display purposes only):

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

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

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

   The authorization server MUST verify the client credentials, the
   validity of the refresh token, and that the resource owner's
   authorization is still valid.  If the request is valid, the
   authorization server issues an access token response as described in
   Section 5.1.5. 4.2.  The authorization server MAY issue a new refresh token
   in which case the client MUST NOT use the previous refresh token and
   replace it with the newly issued refresh token.

5.1.5.

4.2.  Access Token Response

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

   The token response contains the following parameters:

   access_token
         REQUIRED.  The access token issued by the authorization server.

   expires_in
         OPTIONAL.  The duration in seconds of the access token
         lifetime.

   refresh_token
         OPTIONAL.  The refresh token used to obtain new access tokens
         using the same end-user access grant as described in
         Section 5.1.4. 4.1.4.

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

   The 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",
       "expires_in":3600,
       "refresh_token":"8xLOxBtZp8"
     }

5.1.6.

4.3.  Error Response

   If the token request is invalid or unauthorized, the authorization
   server constructs the response by adding the following parameter to
   the entity body of the HTTP response with a a 400 status code (Bad
   Request) using the "application/json" media type:

   error
         REQUIRED.  The error code as described in Section 5.1.6.1. 4.3.1.

   For example:

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

     {
       "error":"incorrect_client_credentials"
     }

5.1.6.1.

4.3.1.  Error Codes

   [[ expalain each error code: ]]

   o  "redirect_uri_mismatch"

   o  "bad_verification_code"  "bad_authorization_code"

   o  "incorrect_client_credentials"  "invalid_client_credentials"

   o  "unauthorized_client'" - The client is not permitted to use this
      authorization
      access grant type.

   o  "invalid_assertion"

   o  "unknown_format"

   o  "authorization_expired"

6.

   o  "multiple_credentials"

   o  "invalid_user_credentials"

5.  Accessing a Protected Resource

   Clients access protected resources by presenting an access token to
   the resource server.

   For example:

     GET /resource HTTP/1.1
     Host: server.example.com
     Authorization: Token token="vF9dft4qmT"

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

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

   Clients SHOULD NOT make authenticated requests with an access token
   to unfamiliar resource servers, especially when using bearer tokens,
   regardless of the presence of a secure channel.

   The methods used by the resource server to validate the access token
   are beyond the scope of this specification, but generally involve an
   interaction or coordination between the resource server and
   authorization server.

   The resource server MUST validate the access token and ensure it has
   not expired and that its scope covers the requested resource.  If the
   token expired or is invalid, the resource server MUST reply with an
   HTTP 401 status code (Unauthorized) and include the HTTP
   "WWW-Authenticate" response header field as described in Section 7.1. 6.

   For example:

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: Token realm='Service', error='token_expired'

   Clients make authenticated token requests using the "Authorization"
   request header field as described in Section 6.1. 5.1.  Alternatively,
   clients MAY include the access token using the HTTP request URI in
   the query component as described in Section 6.2, 5.2, or in the HTTP body
   when using the "application/x-www-form-urlencoded" content type as
   described in Section 6.3. 5.3.

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

6.1.

5.1.  The Authorization Request Header Field

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

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

     credentials    = "Token" RWS access-token [ CS 1#auth-param ]
     access-token   = "token" "=" <"> token <">
     CS             = OWS "," OWS

6.2.

5.2.  URI Query Parameter

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

   For example, the client makes the following HTTPS request:

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

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

   The resource server MUST validate the access token and ensure it has
   not expired and its scope includes the requested resource.  If the
   resource expired or is not valid, the resource server MUST reply with
   an HTTP 401 status code (Unauthorized) and include the HTTP
   "WWW-Authenticate" response header field as described in Section 7.1.

6.3. 6.

5.3.  Form-Encoded Body Parameter

   When including the access token in the HTTP request entity-body, the
   client adds the access token to the request body using the
   "oauth_token" parameter.  The client can use this method only if the
   following REQUIRED conditions are met:

   o  The entity-body is single-part.

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

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

   o  The HTTP request method is "POST", "PUT", or "DELETE".

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

   For example, the client makes the following HTTPS request:

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

     oauth_token=vF9dft4qmT

   The resource server MUST validate the access token and ensure it has
   not expired and its scope includes the requested resource.  If the
   resource expired or is not valid, the resource server MUST reply with
   an HTTP 401 status code (Unauthorized) and include the HTTP
   "WWW-Authenticate" response header field as described in Section 7.1.

7.  Identifying a Protected Resource 6.

6.  The WWW-Authenticate Response Header Field

   Clients access protected resources after locating the appropriate
   end-user authorization endpoint and token endpoint and obtaining an
   access token.  In many cases, interacting with a protected resource
   requires prior knowledge of the protected resource properties and
   methods, as well as its authentication requirements (i.e.
   establishing client identity, locating the end-user authorization and
   token endpoints).

   However, there are cases in which clients are unfamiliar with the
   protected resource, including whether the resource requires
   authentication.  When clients attempt to access an unfamiliar
   protected resource without an access token, the resource server
   denies the request and informs the client of the required credentials
   using an HTTP authentication challenge.

   In addition, when receiving an invalid authenticated request, the
   resource server issues an authentication challenge including the
   error type and message.

7.1.  The WWW-Authenticate Response Header

   A resource server receiving a request for a protected resource
   without a valid access token MUST respond with a 401 (Unauthorized)
   or 403 (Forbidden) HTTP status code, and include at least one "Token"
   "WWW-Authenticate" response header field challenge.

   The "WWW-Authenticate" header field uses the framework defined by
   [RFC2617] as follows:

     challenge       = "Token" RWS token-challenge

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

     error           = "error" "=" <"> token <">

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

   The "error" attribute is used to inform the client the reason why an
   access request was declined. [[ Add list of error codes ]]

8.

7.  Security Considerations

   [[ Todo todo ]]

9.

8.  IANA Considerations

   [[ Not Yet ]]

Appendix A.  Examples

   [[ todo ]]

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, Igor Faynberg, George Fletcher, Evan Gilbert, Justin Hart,
   John Kemp, Torsten Lodderstedt, Eve Maler, James Manger, Chuck
   Mortimore, Justin Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre,
   Marius Scurtescu, Justin Smith, and Franklin Tse.

Appendix B. C.  Acknowledgements

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

Appendix C. D.  Document History

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

   -08

   o  Renamed verification code to authorization code.

   o  Revised terminology, structured section, added new terms.

   o  Changed flows to profiles and moved to introduction.

   o  Added support for access token rescoping.

   o  Cleaned up client credentials section.

   o  New introduction overview.

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

   o  Added access grant type parameter to token endpoint.

   -07

   o  Major rewrite of entire document structure.

   o  Removed device profile.

   o  Added verification code support to user-agent flow.

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

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

   o  Removed "type" parameter from token endpoint.

   -06
   o  Editorial changes, corrections, clarifications, etc.

   o  Removed conformance section.

   o  Moved authors section to contributors appendix.

   o  Added section on native applications.

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

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

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

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

   o  Added figure titles.

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

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

   o  Removed all signature and cryptography.

   o  Removed all discovery.

   o  Updated HTML4 reference.

   -05

   o  Corrected device example.

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

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

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

   o  Change authorization endpoint to end-user endpoint.

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

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

   -04

   o  Changed all token endpoints to use "POST"

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

   o  Changed the flow categories to clarify the autonomous group.

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

   o  Added a "scope" response parameter.

   o  Fixed typos.

   o  Fixed broken document structure.

   -03

   o  Fixed typo in JSON error examples.

   o  Fixed general typos.

   o  Moved all flows sections up one level.

   -02

   o  Removed restriction on "redirect_uri" including a query.

   o  Added "scope" parameter.

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

   -01

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

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

   -00

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

10.

9.  References

10.1.

9.1.  Normative References

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

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

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

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

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

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

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

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

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

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

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

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

   [W3C.REC-html401-19991224]
              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.

9.2.  Informative References

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

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

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

Authors' Addresses

   Eran Hammer-Lahav (editor)
   Yahoo!

   Email: eran@hueniverse.com
   URI:   http://hueniverse.com
   David Recordon
   Facebook

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

   Dick Hardt
   Microsoft

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