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RFC 6749

The OAuth 2.0 Authorization Framework

Pages: 76
Proposed Standard
Errata
Obsoletes:  5849
Updated by:  8252
Part 1 of 4 – Pages 1 to 13
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Top   ToC   RFC6749 - Page 1
Internet Engineering Task Force (IETF)                     D. Hardt, Ed.
Request for Comments: 6749                                     Microsoft
Obsoletes: 5849                                             October 2012
Category: Standards Track
ISSN: 2070-1721


                 The OAuth 2.0 Authorization Framework

Abstract

The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6749. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
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Table of Contents

1. Introduction ....................................................4 1.1. Roles ......................................................6 1.2. Protocol Flow ..............................................7 1.3. Authorization Grant ........................................8 1.3.1. Authorization Code ..................................8 1.3.2. Implicit ............................................8 1.3.3. Resource Owner Password Credentials .................9 1.3.4. Client Credentials ..................................9 1.4. Access Token ..............................................10 1.5. Refresh Token .............................................10 1.6. TLS Version ...............................................12 1.7. HTTP Redirections .........................................12 1.8. Interoperability ..........................................12 1.9. Notational Conventions ....................................13 2. Client Registration ............................................13 2.1. Client Types ..............................................14 2.2. Client Identifier .........................................15 2.3. Client Authentication .....................................16 2.3.1. Client Password ....................................16 2.3.2. Other Authentication Methods .......................17 2.4. Unregistered Clients ......................................17 3. Protocol Endpoints .............................................18 3.1. Authorization Endpoint ....................................18 3.1.1. Response Type ......................................19 3.1.2. Redirection Endpoint ...............................19 3.2. Token Endpoint ............................................21 3.2.1. Client Authentication ..............................22 3.3. Access Token Scope ........................................23 4. Obtaining Authorization ........................................23 4.1. Authorization Code Grant ..................................24 4.1.1. Authorization Request ..............................25 4.1.2. Authorization Response .............................26 4.1.3. Access Token Request ...............................29 4.1.4. Access Token Response ..............................30 4.2. Implicit Grant ............................................31 4.2.1. Authorization Request ..............................33 4.2.2. Access Token Response ..............................35 4.3. Resource Owner Password Credentials Grant .................37 4.3.1. Authorization Request and Response .................39 4.3.2. Access Token Request ...............................39 4.3.3. Access Token Response ..............................40 4.4. Client Credentials Grant ..................................40 4.4.1. Authorization Request and Response .................41 4.4.2. Access Token Request ...............................41 4.4.3. Access Token Response ..............................42 4.5. Extension Grants ..........................................42
Top   ToC   RFC6749 - Page 3
   5. Issuing an Access Token ........................................43
      5.1. Successful Response .......................................43
      5.2. Error Response ............................................45
   6. Refreshing an Access Token .....................................47
   7. Accessing Protected Resources ..................................48
      7.1. Access Token Types ........................................49
      7.2. Error Response ............................................49
   8. Extensibility ..................................................50
      8.1. Defining Access Token Types ...............................50
      8.2. Defining New Endpoint Parameters ..........................50
      8.3. Defining New Authorization Grant Types ....................51
      8.4. Defining New Authorization Endpoint Response Types ........51
      8.5. Defining Additional Error Codes ...........................51
   9. Native Applications ............................................52
   10. Security Considerations .......................................53
      10.1. Client Authentication ....................................53
      10.2. Client Impersonation .....................................54
      10.3. Access Tokens ............................................55
      10.4. Refresh Tokens ...........................................55
      10.5. Authorization Codes ......................................56
      10.6. Authorization Code Redirection URI Manipulation ..........56
      10.7. Resource Owner Password Credentials ......................57
      10.8. Request Confidentiality ..................................58
      10.9. Ensuring Endpoint Authenticity ...........................58
      10.10. Credentials-Guessing Attacks ............................58
      10.11. Phishing Attacks ........................................58
      10.12. Cross-Site Request Forgery ..............................59
      10.13. Clickjacking ............................................60
      10.14. Code Injection and Input Validation .....................60
      10.15. Open Redirectors ........................................60
      10.16. Misuse of Access Token to Impersonate Resource
             Owner in Implicit Flow ..................................61
   11. IANA Considerations ...........................................62
      11.1. OAuth Access Token Types Registry ........................62
           11.1.1. Registration Template .............................62
      11.2. OAuth Parameters Registry ................................63
           11.2.1. Registration Template .............................63
           11.2.2. Initial Registry Contents .........................64
      11.3. OAuth Authorization Endpoint Response Types Registry .....66
           11.3.1. Registration Template .............................66
           11.3.2. Initial Registry Contents .........................67
      11.4. OAuth Extensions Error Registry ..........................67
           11.4.1. Registration Template .............................68
   12. References ....................................................68
      12.1. Normative References .....................................68
      12.2. Informative References ...................................70
Top   ToC   RFC6749 - Page 4
   Appendix A. Augmented Backus-Naur Form (ABNF) Syntax ..............71
     A.1.  "client_id" Syntax ........................................71
     A.2.  "client_secret" Syntax ....................................71
     A.3.  "response_type" Syntax ....................................71
     A.4.  "scope" Syntax ............................................72
     A.5.  "state" Syntax ............................................72
     A.6.  "redirect_uri" Syntax .....................................72
     A.7.  "error" Syntax ............................................72
     A.8.  "error_description" Syntax ................................72
     A.9.  "error_uri" Syntax ........................................72
     A.10. "grant_type" Syntax .......................................73
     A.11. "code" Syntax .............................................73
     A.12. "access_token" Syntax .....................................73
     A.13. "token_type" Syntax .......................................73
     A.14. "expires_in" Syntax .......................................73
     A.15. "username" Syntax .........................................73
     A.16. "password" Syntax .........................................73
     A.17. "refresh_token" Syntax ....................................74
     A.18. Endpoint Parameter Syntax .................................74
   Appendix B. Use of application/x-www-form-urlencoded Media Type ...74
   Appendix C. Acknowledgements ......................................75

1. Introduction

In the traditional client-server authentication model, the client requests an access-restricted resource (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 restricted 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 inherent in 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 the third party's password.
Top   ToC   RFC6749 - Page 5
   o  Compromise of any third-party application results in compromise of
      the end-user's password and all of the data protected by that
      password.

   OAuth addresses these issues by introducing an authorization layer
   and separating the role of the client from that of the resource
   owner.  In OAuth, the client 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 denoting a
   specific scope, lifetime, and other access 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, an end-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 a server trusted by the photo-sharing service
   (authorization server), which issues the printing service delegation-
   specific credentials (access token).

   This specification is designed for use with HTTP ([RFC2616]).  The
   use of OAuth over any protocol other than HTTP is out of scope.

   The OAuth 1.0 protocol ([RFC5849]), published as an informational
   document, was the result of a small ad hoc community effort.  This
   Standards Track specification builds on the OAuth 1.0 deployment
   experience, as well as additional use cases and extensibility
   requirements gathered from the wider IETF community.  The OAuth 2.0
   protocol is not backward compatible with OAuth 1.0.  The two versions
   may co-exist on the network, and implementations may choose to
   support both.  However, it is the intention of this specification
   that new implementations support OAuth 2.0 as specified in this
   document and that OAuth 1.0 is used only to support existing
   deployments.  The OAuth 2.0 protocol shares very few implementation
   details with the OAuth 1.0 protocol.  Implementers familiar with
   OAuth 1.0 should approach this document without any assumptions as to
   its structure and details.
Top   ToC   RFC6749 - Page 6

1.1. Roles

OAuth defines four roles: 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 An application making protected resource requests on behalf of the resource owner and with its authorization. The term "client" does not imply any particular implementation characteristics (e.g., whether the application executes on a server, a desktop, or other devices). authorization server The server issuing access tokens to the client after successfully authenticating the resource owner and obtaining authorization. The interaction between the authorization server and resource server is beyond the scope of this specification. The authorization server may be the same server as the resource server or a separate entity. A single authorization server may issue access tokens accepted by multiple resource servers.
Top   ToC   RFC6749 - Page 7

1.2. Protocol Flow

+--------+ +---------------+ | |--(A)- Authorization Request ->| Resource | | | | Owner | | |<-(B)-- Authorization Grant ---| | | | +---------------+ | | | | +---------------+ | |--(C)-- Authorization Grant -->| Authorization | | Client | | Server | | |<-(D)----- Access Token -------| | | | +---------------+ | | | | +---------------+ | |--(E)----- Access Token ------>| Resource | | | | Server | | |<-(F)--- Protected Resource ---| | +--------+ +---------------+ Figure 1: Abstract Protocol Flow The abstract OAuth 2.0 flow illustrated in Figure 1 describes the interaction between the four roles and includes the following steps: (A) The client requests authorization from the resource owner. The authorization request can be made directly to the resource owner (as shown), or preferably indirectly via the authorization server as an intermediary. (B) The client receives an authorization grant, which is a credential representing the resource owner's authorization, expressed using one of four grant types defined in this specification or using an extension grant type. The authorization grant type depends on the method used by the client to request authorization and the types supported by the authorization server. (C) The client requests an access token by authenticating with the authorization server and presenting the authorization grant. (D) The authorization server authenticates the client and validates the authorization grant, and if valid, issues an access token.
Top   ToC   RFC6749 - Page 8
   (E)  The client requests the protected resource from the resource
        server and authenticates by presenting the access token.

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

   The preferred method for the client to obtain an authorization grant
   from the resource owner (depicted in steps (A) and (B)) is to use the
   authorization server as an intermediary, which is illustrated in
   Figure 3 in Section 4.1.

1.3. Authorization Grant

An authorization grant is a credential representing the resource owner's authorization (to access its protected resources) used by the client to obtain an access token. This specification defines four grant types -- authorization code, implicit, resource owner password credentials, and client credentials -- as well as an extensibility mechanism for defining additional types.

1.3.1. Authorization Code

The authorization code is obtained by using an authorization server as an intermediary between the client and resource owner. Instead of requesting authorization directly from the resource owner, the client directs the resource owner to an authorization server (via its user-agent as defined in [RFC2616]), which in turn directs the resource owner back to the client with the authorization code. Before directing the resource owner back to the client with the authorization code, the authorization server authenticates the resource owner and obtains authorization. Because the resource owner only authenticates with the authorization server, the resource owner's credentials are never shared with the client. The authorization code provides a few important security benefits, such as the ability to authenticate the client, as well as the transmission of the access token directly to the client without passing it through the resource owner's user-agent and potentially exposing it to others, including the resource owner.

1.3.2. Implicit

The implicit grant is a simplified authorization code flow optimized for clients implemented in a browser using a scripting language such as JavaScript. In the implicit flow, instead of issuing the client an authorization code, the client is issued an access token directly
Top   ToC   RFC6749 - Page 9
   (as the result of the resource owner authorization).  The grant type
   is implicit, as no intermediate credentials (such as an authorization
   code) are issued (and later used to obtain an access token).

   When issuing an access token during the implicit grant flow, the
   authorization server does not authenticate the client.  In some
   cases, the client identity can be verified via the redirection URI
   used to deliver the access token to the client.  The access token may
   be exposed to the resource owner or other applications with access to
   the 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 trips required to obtain an
   access token.  However, this convenience should be weighed against
   the security implications of using implicit grants, such as those
   described in Sections 10.3 and 10.16, especially when the
   authorization code grant type is available.

1.3.3. Resource Owner Password Credentials

The resource owner password credentials (i.e., username and password) can be used directly as an authorization grant to obtain an access token. The credentials should only be used when there is a high degree of trust between the resource owner and the client (e.g., the client is part of the device operating system or a highly privileged application), and when other authorization grant types are not available (such as an authorization code). Even though this grant type requires direct client access to the resource owner credentials, the resource owner credentials are used for a single request and are exchanged for an access token. This grant type can eliminate the need for the client to store the resource owner credentials for future use, by exchanging the credentials with a long-lived access token or refresh token.

1.3.4. Client Credentials

The client credentials (or other forms of client authentication) can be used as an authorization grant when the authorization scope is limited to the protected resources under the control of the client, or to protected resources previously arranged with the authorization server. Client credentials are used as an authorization grant typically when the client is acting on its own behalf (the client is also the resource owner) or is requesting access to protected resources based on an authorization previously arranged with the authorization server.
Top   ToC   RFC6749 - Page 10

1.4. Access Token

Access tokens are credentials used to access protected resources. An access token is a string representing an 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 server. The token may denote an identifier used to retrieve the authorization information or may self-contain the authorization information in a verifiable manner (i.e., a token string consisting of some data and a signature). Additional authentication credentials, which are beyond the scope of this specification, may be required in order for the client to use a token. The access token provides an abstraction layer, replacing different authorization constructs (e.g., username and password) with a single token understood by the resource server. This abstraction enables issuing access tokens more restrictive than the authorization grant used to obtain them, as well as removing the resource server's need to understand a wide range of authentication methods. 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 such as [RFC6750].

1.5. Refresh Token

Refresh tokens are credentials used to obtain access tokens. Refresh tokens are issued to the client by the authorization server and are used to obtain a new access token when the current access token becomes invalid or expires, or to obtain additional access tokens with identical or narrower scope (access tokens may have a shorter lifetime and fewer permissions than authorized by the resource owner). Issuing a refresh token is optional at the discretion of the authorization server. If the authorization server issues a refresh token, it is included when issuing an access token (i.e., step (D) in Figure 1). A refresh token is a string representing the authorization granted to the client by the resource owner. The string is usually opaque to the client. The token denotes an identifier used to retrieve the
Top   ToC   RFC6749 - Page 11
   authorization information.  Unlike access tokens, refresh tokens are
   intended for use only with authorization servers and are never sent
   to resource servers.

  +--------+                                           +---------------+
  |        |--(A)------- Authorization Grant --------->|               |
  |        |                                           |               |
  |        |<-(B)----------- Access Token -------------|               |
  |        |               & Refresh Token             |               |
  |        |                                           |               |
  |        |                            +----------+   |               |
  |        |--(C)---- Access Token ---->|          |   |               |
  |        |                            |          |   |               |
  |        |<-(D)- Protected Resource --| Resource |   | Authorization |
  | Client |                            |  Server  |   |     Server    |
  |        |--(E)---- Access Token ---->|          |   |               |
  |        |                            |          |   |               |
  |        |<-(F)- Invalid Token Error -|          |   |               |
  |        |                            +----------+   |               |
  |        |                                           |               |
  |        |--(G)----------- Refresh Token ----------->|               |
  |        |                                           |               |
  |        |<-(H)----------- Access Token -------------|               |
  +--------+           & Optional Refresh Token        +---------------+

               Figure 2: Refreshing an Expired Access Token

   The flow illustrated in Figure 2 includes the following steps:

   (A)  The client requests an access token by authenticating with the
        authorization server and presenting an authorization grant.

   (B)  The authorization server authenticates the client and validates
        the authorization grant, and if valid, issues an access token
        and a refresh token.

   (C)  The client makes a protected resource request to the resource
        server by presenting the 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 access token is invalid, the resource server returns
        an invalid token error.
Top   ToC   RFC6749 - Page 12
   (G)  The client requests a new access token by authenticating with
        the authorization server and presenting the refresh token.  The
        client authentication requirements are based on the client type
        and on the authorization server policies.

   (H)  The authorization server authenticates the client and validates
        the refresh token, and if valid, issues a new access token (and,
        optionally, a new refresh token).

   Steps (C), (D), (E), and (F) are outside the scope of this
   specification, as described in Section 7.

1.6. TLS Version

Whenever Transport Layer Security (TLS) is used by this specification, the appropriate version (or versions) of TLS will vary over time, based on the widespread deployment and known security vulnerabilities. At the time of this writing, TLS version 1.2 [RFC5246] is the most recent version, but has a very limited deployment base and might not be readily available for implementation. TLS version 1.0 [RFC2246] is the most widely deployed version and will provide the broadest interoperability. Implementations MAY also support additional transport-layer security mechanisms that meet their security requirements.

1.7. HTTP Redirections

This specification makes extensive use of HTTP redirections, in which the client or the authorization server directs the resource owner's user-agent to another destination. While the examples in this specification show the use of the HTTP 302 status code, any other method available via the user-agent to accomplish this redirection is allowed and is considered to be an implementation detail.

1.8. Interoperability

OAuth 2.0 provides a rich authorization framework with well-defined security properties. However, as a rich and highly extensible framework with many optional components, on its own, this specification is likely to produce a wide range of non-interoperable implementations. In addition, this specification leaves a few required components partially or fully undefined (e.g., client registration, authorization server capabilities, endpoint discovery). Without
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   these components, clients must be manually and specifically
   configured against a specific authorization server and resource
   server in order to interoperate.

   This framework was designed with the clear expectation that future
   work will define prescriptive profiles and extensions necessary to
   achieve full web-scale interoperability.

1.9. 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 Augmented Backus-Naur Form (ABNF) notation of [RFC5234]. Additionally, the rule URI-reference is included from "Uniform Resource Identifier (URI): Generic Syntax" [RFC3986]. Certain security-related terms are to be understood in the sense defined in [RFC4949]. These terms include, but are not limited to, "attack", "authentication", "authorization", "certificate", "confidentiality", "credential", "encryption", "identity", "sign", "signature", "trust", "validate", and "verify". Unless otherwise noted, all the protocol parameter names and values are case sensitive.


(page 13 continued on part 2)

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