| OAuth Working Group | E. Hammer, Ed. |
| Internet-Draft | D. Recordon |
| Obsoletes: 5849 (if approved) | |
| Intended status: Standards Track | D. Hardt |
| Expires: December 08, 2012 | Microsoft |
| June 8, 2012 |
The OAuth 2.0 Authorization Framework
draft-ietf-oauth-v2-27
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.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 08, 2012.
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.
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:
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 other protocol 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 implementation 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.
OAuth defines four roles:
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.
+--------+ +---------------+
| |--(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 ---| |
+--------+ +---------------+
The abstract flow illustrated in Figure 1 describes the interaction between the four roles and includes the following steps:
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 6.
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.
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, and the transmission of the access token directly to the client without passing it through the resource owner's user-agent, potentially exposing it to others, including the resource owner.
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 (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, especially when the authorization code grant type is available.
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.
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.
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 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.
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 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 +---------------+
The flow illustrated in Figure 2 includes the following steps:
Steps C, D, E, and F are outside the scope of this specification as described in Section 7.
Whenever 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.
This specification makes extensive use of HTTP redirections, in which the client or the authorization server direct 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.
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 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.
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) [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.
Before initiating the protocol, the client registers with the authorization server. The means through which the client registers with the authorization server are beyond the scope of this specification, but typically involve end-user interaction with an HTML registration form.
Client registration does not require a direct interaction between the client and the authorization server. When supported by the authorization server, registration can rely on other means for establishing trust and obtaining the required client properties (e.g. redirection URI, client type). For example, registration can be accomplished using a self-issued or third-party-issued assertion, or by the authorization server performing client discovery using a trusted channel.
When registering a client, the client developer SHALL:
OAuth defines two client types, based on their ability to authenticate securely with the authorization server (i.e. ability to maintain the confidentiality of their client credentials):
The client type designation is based on the authorization server's definition of secure authentication and its acceptable exposure levels of client credentials. The authorization server SHOULD NOT make assumptions about the client type.
A client may be implemented as a distributed set of components, each with a different client type and security context (e.g. a distributed client with both a confidential server-based component and a public browser-based component). If the authorization server does not provide support for such clients, or does not provide guidance with regard to their registration, the client SHOULD register each component as a separate client.
This specification has been designed around the following client profiles:
The authorization server issues the registered client a client identifier - a unique string representing the registration information provided by the client. The client identifier is not a secret; it is exposed to the resource owner, and MUST NOT be used alone for client authentication. The client identifier is unique to the authorization server.
The client identifier string size is left undefined by this specification. The client should avoid making assumptions about the identifier size. The authorization server SHOULD document the size of any identifier it issues.
If the client type is confidential, the client and authorization server establish a client authentication method suitable for the security requirements of the authorization server. The authorization server MAY accept any form of client authentication meeting its security requirements.
Confidential clients are typically issued (or establish) a set of client credentials used for authenticating with the authorization server (e.g. password, public/private key pair).
The authorization server MAY establish a client authentication method with public clients. However, the authorization server MUST NOT rely on public client authentication for the purpose of identifying the client.
The client MUST NOT use more than one authentication method in each request.
Clients in possession of a client password MAY use the HTTP Basic authentication scheme as defined in [RFC2617] to authenticate with the authorization server. The client identifier is used as the username, and the client password is used as the password. The authorization server MUST support the HTTP Basic authentication scheme for authenticating clients which were issued a client password.
For example (extra line breaks are for display purposes only):
Authorization: Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3
Alternatively, the authorization server MAY support including the client credentials in the request body using the following parameters:
Including the client credentials in the request body using the two parameters is NOT RECOMMENDED, and SHOULD be limited to clients unable to directly utilize the HTTP Basic authentication scheme (or other password-based HTTP authentication schemes). The parameters can only be transmitted in the request body and MUST NOT be included in the request URI.
For example, requesting to refresh an access token (Section 6) using the body parameters (extra line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded;charset=UTF-8
grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
&client_id=s6BhdRkqt3&client_secret=7Fjfp0ZBr1KtDRbnfVdmIw
The authorization server MUST require the use of TLS as described in Section 1.6 when sending requests using password authentication.
Since this client authentication method involves a password, the authorization server MUST protect any endpoint utilizing it against brute force attacks.
The authorization server MAY support any suitable HTTP authentication scheme matching its security requirements. When using other authentication methods, the authorization server MUST define a mapping between the client identifier (registration record) and authentication scheme.
This specification does not exclude the use of unregistered clients. However, the use with such clients is beyond the scope of this specification, and requires additional security analysis and review of its interoperability impact.
The authorization process utilizes two authorization server endpoints (HTTP resources):
As well as one client endpoint:
Not every authorization grant type utilizes both endpoints. Extension grant types MAY define additional endpoints as needed.
The authorization endpoint is used to interact with the resource owner and obtain an authorization grant. The authorization server MUST first verify the identity of the resource owner. The way in which the authorization server authenticates the resource owner (e.g. username and password login, session cookies) is beyond the scope of this specification.
The means through which the client obtains the location of the authorization endpoint are beyond the scope of this specification, but the location is typically provided in the service documentation.
The endpoint URI MAY include an application/x-www-form-urlencoded formatted ([W3C.REC-html401-19991224]) query component ([RFC3986] section 3.4), which MUST be retained when adding additional query parameters. The endpoint URI MUST NOT include a fragment component.
Since requests to the authorization endpoint result in user authentication and the transmission of clear-text credentials (in the HTTP response), the authorization server MUST require the use of TLS as described in Section 1.6 when sending requests to the authorization endpoint.
The authorization server MUST support the use of the HTTP GET method [RFC2616] for the authorization endpoint, and MAY support the use of the POST method as well.
Parameters sent without a value MUST be treated as if they were omitted from the request. The authorization server MUST ignore unrecognized request parameters. Request and response parameters MUST NOT be included more than once.
The authorization endpoint is used by the authorization code grant type and implicit grant type flows. The client informs the authorization server of the desired grant type using the following parameter:
Extension response types MAY contain a space-delimited (%x20) list of values, where the order of values does not matter (e.g. response type a b is the same as b a). The meaning of such composite response types is defined by their respective specifications.
If an authorization request is missing the response_type parameter, or if the response type is not understood, the authorization server MUST return an error response as described in Section 4.1.2.1.
After completing its interaction with the resource owner, the authorization server directs the resource owner's user-agent back to the client. The authorization server redirects the user-agent to the client's redirection endpoint previously established with the authorization server during the client registration process or when making the authorization request.
The redirection endpoint URI MUST be an absolute URI as defined by [RFC3986] section 4.3. The endpoint URI MAY include an application/x-www-form-urlencoded formatted ([W3C.REC-html401-19991224]) query component ([RFC3986] section 3.4), which MUST be retained when adding additional query parameters. The endpoint URI MUST NOT include a fragment component.
The redirection endpoint SHOULD require the use of TLS as described in Section 1.6 when the requested response type is code or token, or when the redirection request will result in the transmission of sensitive credentials over an open network. This specification does not mandate the use of TLS because at the time of this writing, requiring clients to deploy TLS is a significant hurdle for many client developers. If TLS is not available, the authorization server SHOULD warn the resource owner about the insecure endpoint prior to redirection (e.g. display a message during the authorization request).
Lack of transport-layer security can have a severe impact on the security of the client and the protected resources it is authorized to access. The use of transport-layer security is particularly critical when the authorization process is used as a form of delegated end-user authentication by the client (e.g. third-party sign-in service).
The authorization server MUST require the following clients to register their redirection endpoint:
The authorization server SHOULD require all clients to register their redirection endpoint prior to utilizing the authorization endpoint.
The authorization server SHOULD require the client to provide the complete redirection URI (the client MAY use the state request parameter to achieve per-request customization). If requiring the registration of the complete redirection URI is not possible, the authorization server SHOULD require the registration of the URI scheme, authority, and path (allowing the client to dynamically vary only the query component of the redirection URI when requesting authorization).
The authorization server MAY allow the client to register multiple redirection endpoints.
Lack of a redirection URI registration requirement can enable an attacker to use the authorization endpoint as open redirector as described in Section 10.15.
If multiple redirection URIs have been registered, if only part of the redirection URI has been registered, or if no redirection URI has been registered, the client MUST include a redirection URI with the authorization request using the redirect_uri request parameter.
When a redirection URI is included in an authorization request, the authorization server MUST compare and match the value received against at least one of the registered redirection URIs (or URI components) as defined in [RFC3986] section 6, if any redirection URIs were registered. If the client registration included the full redirection URI, the authorization server MUST compare the two URIs using simple string comparison as defined in [RFC3986] section 6.2.1.
If an authorization request fails validation due to a missing, invalid, or mismatching redirection URI, the authorization server SHOULD inform the resource owner of the error, and MUST NOT automatically redirect the user-agent to the invalid redirection URI.
The redirection request to the client's endpoint typically results in an HTML document response, processed by the user-agent. If the HTML response is served directly as the result of the redirection request, any script included in the HTML document will execute with full access to the redirection URI and the credentials it contains.
The client SHOULD NOT include any third-party scripts (e.g. third-party analytics, social plug-ins, ad networks) in the redirection endpoint response. Instead, it SHOULD extract the credentials from the URI and redirect the user-agent again to another endpoint without exposing the credentials (in the URI or elsewhere). If third-party scripts are included, the client MUST ensure that its own scripts (used to extract and remove the credentials from the URI) will execute first.
The token endpoint is used by the client to obtain an access token by presenting its authorization grant or refresh token. The token endpoint is used with every authorization grant except for the implicit grant type (since an access token is issued directly).
The means through which the client obtains the location of the token endpoint are beyond the scope of this specification but is typically provided in the service documentation.
The endpoint URI MAY include an application/x-www-form-urlencoded formatted ([W3C.REC-html401-19991224]) query component ([RFC3986] section 3.4), which MUST be retained when adding additional query parameters. The endpoint URI MUST NOT include a fragment component.
Since requests to the token endpoint result in the transmission of clear-text credentials (in the HTTP request and response), the authorization server MUST require the use of TLS as described in Section 1.6 when sending requests to the token endpoint.
The client MUST use the HTTP POST method when making access token requests.
Parameters sent without a value MUST be treated as if they were omitted from the request. The authorization server MUST ignore unrecognized request parameters. Request and response parameters MUST NOT be included more than once.
Confidential clients or other clients issued client credentials MUST authenticate with the authorization server as described in Section 2.3 when making requests to the token endpoint. Client authentication is used for:
A public client that was not issued a client password MAY use the client_id request parameter to identify itself when sending requests to the token endpoint (e.g. for the purpose of providing end-user context, client usage statistics).
The authorization and token endpoints allow the client to specify the scope of the access request using the scope request parameter. In turn, the authorization server uses the scope response parameter to inform the client of the scope of the access token issued.
The value of the scope parameter is expressed as a list of space-delimited, case sensitive strings. The strings are 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.
scope = scope-token *( SP scope-token )
scope-token = 1*( %x21 / %x23-5B / %x5D-7E )
The authorization server MAY fully or partially ignore the scope requested by the client based on the authorization server policy or the resource owner's instructions. If the issued access token scope is different from the one requested by the client, the authorization server MUST include the scope response parameter to inform the client of the actual scope granted.
If the client omits the scope parameter when requesting authorization, the authorization server MUST either process the request using a pre-defined default value, or fail the request indicating an invalid scope. The authorization server SHOULD document its scope requirements and default value (if defined).
To request an access token, the client obtains authorization from the resource owner. The authorization is expressed in the form of an authorization grant which the client uses to request the access token. OAuth defines four grant types: authorization code, implicit, resource owner password credentials, and client credentials. It also provides an extension mechanism for defining additional grant types.
The authorization code grant type is used to obtain both access tokens and refresh tokens and is optimized for confidential clients. As a redirection-based flow, the client must be capable of interacting with the resource owner's user-agent (typically a web browser) and capable of receiving incoming requests (via redirection) from the authorization server.
+----------+
| resource |
| owner |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +---------------+
| -+----(A)-- & Redirection URI ---->| |
| User- | | Authorization |
| Agent -+----(B)-- User authenticates --->| Server |
| | | |
| -+----(C)-- Authorization Code ---<| |
+-|----|---+ +---------------+
| | ^ v
(A) (C) | |
| | | |
^ v | |
+---------+ | |
| |>---(D)-- Authorization Code ---------' |
| Client | & Redirection URI |
| | |
| |<---(E)----- Access Token -------------------'
+---------+ (w/ Optional Refresh Token)
Note: The lines illustrating steps A, B, and C are broken into two parts as they pass through the user-agent.
The flow illustrated in Figure 6 includes the following steps:
The client constructs the request URI by adding the following parameters to the query component of the authorization endpoint URI using the application/x-www-form-urlencoded format as defined by [W3C.REC-html401-19991224]:
The client directs the resource owner to the constructed URI using an HTTP redirection response, or by other means available to it via the user-agent.
For example, the client directs the user-agent to make the following HTTP request using TLS (extra line breaks are for display purposes only):
GET /authorize?response_type=code&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com
The authorization server validates the request to ensure all required parameters are present and valid. If the request is valid, the authorization server authenticates the resource owner and obtains an authorization decision (by asking the resource owner or by establishing approval via other means).
When a decision is established, the authorization server directs the user-agent to the provided client redirection URI using an HTTP redirection response, or by other means available to it via the user-agent.
If the resource owner grants the access request, the authorization server issues an authorization code and delivers it to the client by adding the following parameters to the query component of the redirection URI using the application/x-www-form-urlencoded format:
For example, the authorization server redirects the user-agent by sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=SplxlOBeZQQYbYS6WxSbIA
&state=xyz
The client MUST ignore unrecognized response parameters. The authorization code string size is left undefined by this specification. The client should avoid making assumptions about code value sizes. The authorization server SHOULD document the size of any value it issues.
If the request fails due to a missing, invalid, or mismatching redirection URI, or if the client identifier is missing or invalid, the authorization server SHOULD inform the resource owner of the error, and MUST NOT automatically redirect the user-agent to the invalid redirection URI.
If the resource owner denies the access request or if the request fails for reasons other than a missing or invalid redirection URI, the authorization server informs the client by adding the following parameters to the query component of the redirection URI using the application/x-www-form-urlencoded format:
Values for the
error parameter MUST NOT include characters outside the set %x20-21 / %x23-5B / %x5D-7E.
For example, the authorization server redirects the user-agent by sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied&state=xyz
The client makes a request to the token endpoint by adding the following parameters using the application/x-www-form-urlencoded format in the HTTP request entity-body:
If the client type is confidential or the client was issued client credentials (or assigned other authentication requirements), the client MUST authenticate with the authorization server as described in Section 3.2.1.
For example, the client makes the following HTTP request using TLS (extra 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;charset=UTF-8
grant_type=authorization_code&code=SplxlOBeZQQYbYS6WxSbIA
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
The authorization server MUST:
If the access token request is valid and authorized, the authorization server issues an access token and optional refresh token as described in Section 5.1. If the request client authentication failed or is invalid, the authorization server returns an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"example",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter":"example_value"
}
The implicit grant type is used to obtain access tokens (it does not support the issuance of refresh tokens) and is optimized for public clients known to operate a particular redirection URI. These clients are typically implemented in a browser using a scripting language such as JavaScript.
As a redirection-based flow, the client must be capable of interacting with the resource owner's user-agent (typically a web browser) and capable of receiving incoming requests (via redirection) from the authorization server.
Unlike the authorization code grant type in which the client makes separate requests for authorization and access token, the client receives the access token as the result of the authorization request.
The implicit grant type does not include client authentication, and relies on the presence of the resource owner and the registration of the redirection URI. Because the access token is encoded into the redirection URI, it may be exposed to the resource owner and other applications residing on the same device.
+----------+
| Resource |
| Owner |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +---------------+
| -+----(A)-- & Redirection URI --->| |
| User- | | Authorization |
| Agent -|----(B)-- User authenticates -->| Server |
| | | |
| |<---(C)--- Redirection URI ----<| |
| | with Access Token +---------------+
| | in Fragment
| | +---------------+
| |----(D)--- Redirection URI ---->| Web-Hosted |
| | without Fragment | Client |
| | | Resource |
| (F) |<---(E)------- Script ---------<| |
| | +---------------+
+-|--------+
| |
(A) (G) Access Token
| |
^ v
+---------+
| |
| Client |
| |
+---------+
Note: The lines illustrating steps A and B are broken into two parts as they pass through the user-agent.
The flow illustrated in Figure 12 includes the following steps:
The client constructs the request URI by adding the following parameters to the query component of the authorization endpoint URI using the application/x-www-form-urlencoded format:
The client directs the resource owner to the constructed URI using an HTTP redirection response, or by other means available to it via the user-agent.
For example, the client directs the user-agent to make the following HTTP request using TLS (extra line breaks are for display purposes only):
GET /authorize?response_type=token&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com
The authorization server validates the request to ensure all required parameters are present and valid. The authorization server MUST verify that the redirection URI to which it will redirect the access token matches a redirection URI registered by the client as described in Section 3.1.2.
If the request is valid, the authorization server authenticates the resource owner and obtains an authorization decision (by asking the resource owner or by establishing approval via other means).
When a decision is established, the authorization server directs the user-agent to the provided client redirection URI using an HTTP redirection response, or by other means available to it via the user-agent.
If the resource owner grants the access request, the authorization server issues an access token and delivers it to the client by adding the following parameters to the fragment component of the redirection URI using the application/x-www-form-urlencoded format:
The authorization server MUST NOT issue a refresh token.
For example, the authorization server redirects the user-agent by sending the following HTTP response (URI extra line breaks are for display purposes only):
HTTP/1.1 302 Found
Location: http://example.com/cb#access_token=2YotnFZFEjr1zCsicMWpAA
&state=xyz&token_type=example&expires_in=3600
Developers should note that some user-agents do not support the inclusion of a fragment component in the HTTP Location response header field. Such clients will require using other methods for redirecting the client than a 3xx redirection response. For example, returning an HTML page which includes a 'continue' button with an action linked to the redirection URI.
The client MUST ignore unrecognized response parameters. The access token string size is left undefined by this specification. The client should avoid making assumptions about value sizes. The authorization server SHOULD document the size of any value it issues.
If the request fails due to a missing, invalid, or mismatching redirection URI, or if the client identifier is missing or invalid, the authorization server SHOULD inform the resource owner of the error, and MUST NOT automatically redirect the user-agent to the invalid redirection URI.
If the resource owner denies the access request or if the request fails for reasons other than a missing or invalid redirection URI, the authorization server informs the client by adding the following parameters to the fragment component of the redirection URI using the application/x-www-form-urlencoded format:
Values for the
error parameter MUST NOT include characters outside the set %x20-21 / %x23-5B / %x5D-7E.
For example, the authorization server redirects the user-agent by sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb#error=access_denied&state=xyz
The resource owner password credentials grant type is suitable in cases where the resource owner has a trust relationship with the client, such as the device operating system or a highly privileged application. The authorization server should take special care when enabling this grant type, and only allow it when other flows are not viable.
The grant type is suitable for clients capable of obtaining the resource owner's credentials (username and password, typically using an interactive form). It is also used to migrate existing clients using direct authentication schemes such as HTTP Basic or Digest authentication to OAuth by converting the stored credentials to an access token.
+----------+
| Resource |
| Owner |
| |
+----------+
v
| Resource Owner
(A) Password Credentials
|
v
+---------+ +---------------+
| |>--(B)---- Resource Owner ------->| |
| | Password Credentials | Authorization |
| Client | | Server |
| |<--(C)---- Access Token ---------<| |
| | (w/ Optional Refresh Token) | |
+---------+ +---------------+
The flow illustrated in Figure 16 includes the following steps:
The method through which the client obtains the resource owner credentials is beyond the scope of this specification. The client MUST discard the credentials once an access token has been obtained.
The client makes a request to the token endpoint by adding the following parameters using the application/x-www-form-urlencoded format in the HTTP request entity-body:
If the client type is confidential or the client was issued client credentials (or assigned other authentication requirements), the client MUST authenticate with the authorization server as described in Section 3.2.1.
For example, the client makes the following HTTP request using transport-layer security (extra 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;charset=UTF-8
grant_type=password&username=johndoe&password=A3ddj3w
The authorization server MUST:
Since this access token request utilizes the resource owner's password, the authorization server MUST protect the endpoint against brute force attacks (e.g. using rate-limitation or generating alerts).
If the access token request is valid and authorized, the authorization server issues an access token and optional refresh token as described in Section 5.1. If the request failed client authentication or is invalid, the authorization server returns an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"example",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter":"example_value"
}
The client can request an access token using only its client credentials (or other supported means of authentication) when the client is requesting access to the protected resources under its control, or those of another resource owner which has been previously arranged with the authorization server (the method of which is beyond the scope of this specification).
The client credentials grant type MUST only be used by confidential clients.
+---------+ +---------------+
| | | |
| |>--(A)- Client Authentication --->| Authorization |
| Client | | Server |
| |<--(B)---- Access Token ---------<| |
| | | |
+---------+ +---------------+
The flow illustrated in Figure 19 includes the following steps:
Since the client authentication is used as the authorization grant, no additional authorization request is needed.
The client makes a request to the token endpoint by adding the following parameters using the application/x-www-form-urlencoded format in the HTTP request entity-body:
The client MUST authenticate with the authorization server as described in Section 3.2.1.
For example, the client makes the following HTTP request using transport-layer security (extra 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;charset=UTF-8
grant_type=client_credentials
The authorization server MUST authenticate the client.
If the access token request is valid and authorized, the authorization server issues an access token as described in Section 5.1. A refresh token SHOULD NOT be included. If the request failed client authentication or is invalid, the authorization server returns an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"example",
"expires_in":3600,
"example_parameter":"example_value"
}
The client uses an extension grant type by specifying the grant type using an absolute URI (defined by the authorization server) as the value of the grant_type parameter of the token endpoint, and by adding any additional parameters necessary.
For example, to request an access token using a SAML 2.0 assertion grant type as defined by [I-D.ietf-oauth-saml2-bearer], the client makes the following HTTP request using TLS (line breaks are for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded;charset=UTF-8
grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Asaml2-
bearer&assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ9IjIwMTEtMDU
[...omitted for brevity...]aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-
If the access token request is valid and authorized, the authorization server issues an access token and optional refresh token as described in Section 5.1. If the request failed client authentication or is invalid, the authorization server returns an error response as described in Section 5.2.
If the access token request is valid and authorized, the authorization server issues an access token and optional refresh token as described in Section 5.1. If the request failed client authentication or is invalid, the authorization server returns an error response as described in Section 5.2.
The authorization server issues an access token and optional refresh token, and constructs the response by adding the following parameters to the entity body of the HTTP response with a 200 (OK) status code:
The parameters are included 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 order of parameters does not matter and can vary.
The authorization server MUST include the HTTP Cache-Control response header field [RFC2616] with a value of no-store in any response containing tokens, credentials, or other sensitive information, as well as the Pragma response header field [RFC2616] with a value of no-cache.
For example:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"example",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter":"example_value"
}
The client MUST ignore unrecognized value names in the response. The sizes of tokens and other values received from the authorization server are left undefined. The client should avoid making assumptions about value sizes. The authorization server SHOULD document the size of any value it issues.
The authorization server responds with an HTTP 400 (Bad Request) status code (unless specified otherwise) and includes the following parameters with the response:
Values for the
error parameter MUST NOT include characters outside the set %x20-21 / %x23-5B / %x5D-7E.
The parameters are included 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 order of parameters does not matter and can vary.
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"error":"invalid_request"
}
If the authorization server issued a refresh token to the client, the client makes a refresh request to the token endpoint by adding the following parameters using the application/x-www-form-urlencoded format in the HTTP request entity-body:
Because refresh tokens are typically long-lasting credentials used to request additional access tokens, the refresh token is bound to the client which it was issued. If the client type is confidential or the client was issued client credentials (or assigned other authentication requirements), the client MUST authenticate with the authorization server as described in Section 3.2.1.
For example, the client makes the following HTTP request using transport-layer security (extra 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;charset=UTF-8
grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
The authorization server MUST:
If valid and authorized, the authorization server issues an access token as described in Section 5.1. If the request failed verification or is invalid, the authorization server returns an error response as described in Section 5.2.
The authorization server MAY issue a new refresh token, in which case the client MUST discard the old refresh token and replace it with the new refresh token. The authorization server MAY revoke the old refresh token after issuing a new refresh token to the client. If a new refresh token is issued, the refresh token scope MUST be identical to that of the refresh token included by the client in the request.
The client accesses protected resources by presenting the access token to the resource server. The resource server MUST validate the access token and ensure it has not expired and that its scope covers the requested resource. The methods used by the resource server to validate the access token (as well as any error responses) are beyond the scope of this specification, but generally involve an interaction or coordination between the resource server and the authorization server.
The method in which the client utilizes the access token to authenticate with the resource server depends on the type of access token issued by the authorization server. Typically, it involves using the HTTP Authorization request header field [RFC2617] with an authentication scheme defined by the access token type specification.
The access token type provides the client with the information required to successfully utilize the access token to make a protected resource request (along with type-specific attributes). The client MUST NOT use an access token if it does not understand the token type.
For example, the bearer token type defined in [I-D.ietf-oauth-v2-bearer] is utilized by simply including the access token string in the request:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: Bearer mF_9.B5f-4.1JqM
while the mac token type defined in [I-D.ietf-oauth-v2-http-mac] is utilized by issuing a MAC key together with the access token which is used to sign certain components of the HTTP requests:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: MAC id="h480djs93hd8",
nonce="274312:dj83hs9s",
mac="kDZvddkndxvhGRXZhvuDjEWhGeE="
The above examples are provided for illustration purposes only. Developers are advised to consult the [I-D.ietf-oauth-v2-bearer] and [I-D.ietf-oauth-v2-http-mac] specifications before use.
Each access token type definition specifies the additional attributes (if any) sent to the client together with the access_token response parameter. It also defines the HTTP authentication method used to include the access token when making a protected resource request.
If a resource access request fails, the resource server SHOULD inform the client of the error. While the specific error responses possible and methods for transmitting those errors when using any particular access token type are beyond the scope of this specification, any error code values defined for use with OAuth resource access methods MUST be registered (following the procedures in Section 11.4).
Specifically, when the OAuth resource access method uses an error result parameter to return an error code value that indicates the resource access error encountered, then these error code values MUST be registered. Values for these error codes MUST NOT include characters outside the set %x20-21 / %x23-5B / %x5D-7E. When an error code value is registered for use by an OAuth resource access method, should that same code already be registered for use by another OAuth resource access method or at a different OAuth error usage location, then the meaning of that error code value in in the new registration MUST be consistent with the its meaning in prior registrations.
The OAuth resource access error registration requirement applies only to error code values and not to other means of returning error indications, including HTTP status codes, or other error-related result parameters, such as error_description, error_uri, or other kinds of error status return methods that may be employed by the resource access method. There is no requirement that OAuth resource access methods employ an error parameter.
Access token types can be defined in one of two ways: registered in the access token type registry (following the procedures in Section 11.1), or by using a unique absolute URI as its name.
Types utilizing a URI name SHOULD be limited to vendor-specific implementations that are not commonly applicable, and are specific to the implementation details of the resource server where they are used.
All other types MUST be registered. Type names MUST conform to the type-name ABNF. If the type definition includes a new HTTP authentication scheme, the type name SHOULD be identical to the HTTP authentication scheme name (as defined by [RFC2617]). The token type example is reserved for use in examples.
type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
New request or response parameters for use with the authorization endpoint or the token endpoint are defined and registered in the parameters registry following the procedure in Section 11.2.
Parameter names MUST conform to the param-name ABNF and parameter values syntax MUST be well-defined (e.g., using ABNF, or a reference to the syntax of an existing parameter).
param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
Unregistered vendor-specific parameter extensions that are not commonly applicable, and are specific to the implementation details of the authorization server where they are used SHOULD utilize a vendor-specific prefix that is not likely to conflict with other registered values (e.g. begin with 'companyname_').
New authorization grant types can be defined by assigning them a unique absolute URI for use with the grant_type parameter. If the extension grant type requires additional token endpoint parameters, they MUST be registered in the OAuth parameters registry as described by Section 11.2.
New response types for use with the authorization endpoint are defined and registered in the authorization endpoint response type registry following the procedure in Section 11.3. Response type names MUST conform to the response-type ABNF.
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = "_" / DIGIT / ALPHA
If a response type contains one or more space characters (%x20), it is compared as a space-delimited list of values in which the order of values does not matter. Only one order of values can be registered, which covers all other arrangements of the same set of values.
For example, the response type token code is left undefined by this specification. However, an extension can define and register the token code response type. Once registered, the same combination cannot be registered as code token, but both values can be used to denote the same response type.
In cases where protocol extensions (i.e. access token types, extension parameters, or extension grant types) require additional error codes to be used with the authorization code grant error response (Section 4.1.2.1), the implicit grant error response (Section 4.2.2.1), the token error response (Section 5.2), or the resource access error response (Section 7.2), such error codes MAY be defined.
Extension error codes MUST be registered (following the procedures in Section 11.4) if the extension they are used in conjunction with is a registered access token type, a registered endpoint parameter, or an extension grant type. Error codes used with unregistered extensions MAY be registered.
Error codes MUST conform to the error ABNF, and SHOULD be prefixed by an identifying name when possible. For example, an error identifying an invalid value set to the extension parameter example SHOULD be named example_invalid.
error = 1*error-char
error-char = %x20-21 / %x23-5B / %x5D-7E
Native applications are clients installed and executed on the device used by the resource owner (i.e. desktop application, native mobile application). Native applications require special consideration related to security, platform capabilities, and overall end-user experience.
The authorization endpoint requires interaction between the client and the resource owner's user-agent. Native applications can invoke an external user-agent or embed a user-agent within the application. For example:
When choosing between an external or embedded user-agent, developers should consider:
When choosing between the implicit grant type and the authorization code grant type, the following should be considered:
As a flexible and extensible framework, OAuth's security considerations depend on many factors. The following sections provide implementers with security guidelines focused on the three client profiles described in Section 2.1: web application, user-agent-based application, and native application.
A comprehensive OAuth security model and analysis, as well as background for the protocol design is provided by [I-D.ietf-oauth-v2-threatmodel].
The authorization server establishes client credentials with web application clients for the purpose of client authentication. The authorization server is encouraged to consider stronger client authentication means than a client password. Web application clients MUST ensure confidentiality of client passwords and other client credentials.
The authorization server MUST NOT issue client passwords or other client credentials to native application or user-agent-based application clients for the purpose of client authentication. The authorization server MAY issue a client password or other credentials for a specific installation of a native application client on a specific device.
When client authentication is not possible, the authorization server SHOULD employ other means to validate the client's identity. For example, by requiring the registration of the client redirection URI or enlisting the resource owner to confirm identity. A valid redirection URI is not sufficient to verify the client's identity when asking for resource owner authorization, but can be used to prevent delivering credentials to a counterfeit client after obtaining resource owner authorization.
The authorization server must consider the security implications of interacting with unauthenticated clients and take measures to limit the potential exposure of other credentials (e.g. refresh tokens) issued to such clients.
A malicious client can impersonate another client and obtain access to protected resources, if the impersonated client fails to, or is unable to, keep its client credentials confidential.
The authorization server MUST authenticate the client whenever possible. If the authorization server cannot authenticate the client due to the client's nature, the authorization server MUST require the registration of any redirection URI used for receiving authorization responses, and SHOULD utilize other means to protect resource owners from such potentially malicious clients. For example, the authorization server can engage the resource owner to assist in identifying the client and its origin.
The authorization server SHOULD enforce explicit resource owner authentication and provide the resource owner with information about the client and the requested authorization scope and lifetime. It is up to the resource owner to review the information in the context of the current client, and authorize or deny the request.
The authorization server SHOULD NOT process repeated authorization requests automatically (without active resource owner interaction) without authenticating the client or relying on other measures to ensure the repeated request comes from the original client and not an impersonator.
Access token credentials (as well as any confidential access token attributes) MUST be kept confidential in transit and storage, and only shared among the authorization server, the resource servers the access token is valid for, and the client to whom the access token is issued. Access token credentials MUST only be transmitted using TLS as described in Section 1.6 with server authentication as defined by [RFC2818].
When using the implicit grant type, the access token is transmitted in the URI fragment, which can expose it to unauthorized parties.
The authorization server MUST ensure that access tokens cannot be generated, modified, or guessed to produce valid access tokens by unauthorized parties.
The client SHOULD request access tokens with the minimal scope necessary. The authorization server SHOULD take the client identity into account when choosing how to honor the requested scope, and MAY issue an access token with a less rights than requested.
This specification does not provide any methods for the resource server to ensure that an access token presented to it by a given client was issued to that client by the authorization server.
Authorization servers MAY issue refresh tokens to web application clients and native application clients.
Refresh tokens MUST be kept confidential in transit and storage, and shared only among the authorization server and the client to whom the refresh tokens were issued. The authorization server MUST maintain the binding between a refresh token and the client to whom it was issued. Refresh tokens MUST only be transmitted using TLS as described in Section 1.6 with server authentication as defined by [RFC2818].
The authorization server MUST verify the binding between the refresh token and client identity whenever the client identity can be authenticated. When client authentication is not possible, the authorization server SHOULD deploy other means to detect refresh token abuse.
For example, the authorization server could employ refresh token rotation in which a new refresh token is issued with every access token refresh response. The previous refresh token is invalidated but retained by the authorization server. If a refresh token is compromised and subsequently used by both the attacker and the legitimate client, one of them will present an invalidated refresh token which will inform the authorization server of the breach.
The authorization server MUST ensure that refresh tokens cannot be generated, modified, or guessed to produce valid refresh tokens by unauthorized parties.
The transmission of authorization codes SHOULD be made over a secure channel, and the client SHOULD require the use of TLS with its redirection URI if the URI identifies a network resource. Since authorization codes are transmitted via user-agent redirections, they could potentially be disclosed through user-agent history and HTTP referrer headers.
Authorization codes operate as plaintext bearer credentials, used to verify that the resource owner who granted authorization at the authorization server is the same resource owner returning to the client to complete the process. Therefore, if the client relies on the authorization code for its own resource owner authentication, the client redirection endpoint MUST require the use of TLS.
Authorization codes MUST be short lived and single use. If the authorization server observes multiple attempts to exchange an authorization code for an access token, the authorization server SHOULD attempt to revoke all access tokens already granted based on the compromised authorization code.
If the client can be authenticated, the authorization servers MUST authenticate the client and ensure that the authorization code was issued to the same client.
When requesting authorization using the authorization code grant type, the client can specify a redirection URI via the redirect_uri parameter. If an attacker can manipulate the value of the redirection URI, it can cause the authorization server to redirect the resource owner user-agent to a URI under the control of the attacker with the authorization code.
An attacker can create an account at a legitimate client and initiate the authorization flow. When the attacker's user-agent is sent to the authorization server to grant access, the attacker grabs the authorization URI provided by the legitimate client, and replaces the client's redirection URI with a URI under the control of the attacker. The attacker then tricks the victim into following the manipulated link to authorize access to the legitimate client.
Once at the authorization server, the victim is prompted with a normal, valid request on behalf of a legitimate and trusted client, and authorizes the request. The victim is then redirected to an endpoint under the control of the attacker with the authorization code. The attacker completes the authorization flow by sending the authorization code to the client using the original redirection URI provided by the client. The client exchanges the authorization code with an access token and links it to the attacker's client account which can now gain access to the protected resources authorized by the victim (via the client).
In order to prevent such an attack, the authorization server MUST ensure that the redirection URI used to obtain the authorization code is identical to the redirection URI provided when exchanging the authorization code for an access token. The authorization server MUST require public clients and SHOULD require confidential clients to register their redirection URIs. If a redirection URI is provided in the request, the authorization server MUST validate it against the registered value.
The resource owner password credentials grant type is often used for legacy or migration reasons. It reduces the overall risk of storing username and password by the client, but does not eliminate the need to expose highly privileged credentials to the client.
This grant type carries a higher risk than other grant types because it maintains the password anti-pattern this protocol seeks to avoid. The client could abuse the password or the password could unintentionally be disclosed to an attacker (e.g. via log files or other records kept by the client).
Additionally, because the resource owner does not have control over the authorization process (the resource owner involvement ends when it hands over its credentials to the client), the client can obtain access tokens with a broader scope than desired by the resource owner. The authorization server should consider the scope and lifetime of access tokens issued via this grant type.
The authorization server and client SHOULD minimize use of this grant type and utilize other grant types whenever possible.
Access tokens, refresh tokens, resource owner passwords, and client credentials MUST NOT be transmitted in the clear. Authorization codes SHOULD NOT be transmitted in the clear.
The state and scope parameters SHOULD NOT include sensitive client or resource owner information in plain text as they can be transmitted over insecure channels or stored insecurely.
In order to prevent man-in-the-middle attacks, the authorization server MUST require the use of TLS with server authentication as defined by [RFC2818] for any request sent to the authorization and token endpoints. The client MUST validate the authorization server's TLS certificate as defined by [RFC6125], and in accordance with its requirements for server identity authentication.
The authorization server MUST prevent attackers from guessing access tokens, authorization codes, refresh tokens, resource owner passwords, and client credentials.
The probability of an attacker guessing generated tokens (and other credentials not intended for handling by end-users) MUST be less than or equal to 2^(-128) and SHOULD be less than or equal to 2^(-160).
The authorization server MUST utilize other means to protect credentials intended for end-user usage.
Wide deployment of this and similar protocols may cause end-users to become inured to the practice of being redirected to websites where they are asked to enter their passwords. If end-users are not careful to verify the authenticity of these websites before entering their credentials, it will be possible for attackers to exploit this practice to steal resource owners' passwords.
Service providers should attempt to educate end-users about the risks phishing attacks pose, and should provide mechanisms that make it easy for end-users to confirm the authenticity of their sites. Client developers should consider the security implications of how they interact with the user-agent (e.g., external, embedded), and the ability of the end-user to verify the authenticity of the authorization server.
To reduce the risk of phishing attacks, the authorization servers MUST require the use of TLS on every endpoint used for end-user interaction.
Cross-site request forgery (CSRF) is an exploit in which an attacker causes the user-agent of a victim end-user to follow a malicious URI (e.g. provided to the user-agent as a misleading link, image, or redirection) to a trusting server (usually established via the presence of a valid session cookie).
A CSRF attack against the client's redirection URI allows an attacker to inject their own authorization code or access token, which can result in the client using an access token associated with the attacker's protected resources rather than the victim's (e.g. save the victim's bank account information to a protected resource controlled by the attacker).
The client MUST implement CSRF protection for its redirection URI. This is typically accomplished by requiring any request sent to the redirection URI endpoint to include a value that binds the request to the user-agent's authenticated state (e.g. a hash of the session cookie used to authenticate the user-agent). The client SHOULD utilize the state request parameter to deliver this value to the authorization server when making an authorization request.
Once authorization has been obtained from the end-user, the authorization server redirects the end-user's user-agent back to the client with the required binding value contained in the state parameter. The binding value enables the client to verify the validity of the request by matching the binding value to the user-agent's authenticated state. The binding value used for CSRF protection MUST contain a non-guessable value (as described in Section 10.10), and the user-agent's authenticated state (e.g. session cookie, HTML5 local storage) MUST be kept in a location accessible only to the client and the user-agent (i.e., protected by same-origin policy).
A CSRF attack against the authorization server's authorization endpoint can result in an attacker obtaining end-user authorization for a malicious client without involving or alerting the end-user.
The authorization server MUST implement CSRF protection for its authorization endpoint, and ensure that a malicious client cannot obtain authorization without the awareness and explicit consent of the resource owner.
In a clickjacking attack, an attacker registers a legitimate client and then constructs a malicious site in which it loads the authorization server's authorization endpoint web page in a transparent iframe overlaid on top of a set of dummy buttons which are carefully constructed to be placed directly under important buttons on the authorization page. When an end-user clicks a misleading visible button, the end-user is actually clicking an invisible button on the authorization page (such as an "Authorize" button). This allows an attacker to trick a resource owner into granting its client access without their knowledge.
To prevent this form of attack, native applications SHOULD use external browsers instead of embedding browsers within the application when requesting end-user authorization. For most newer browsers, avoidance of iframes can be enforced by the authorization server using the (non-standard) x-frame-options header. This header can have two values, deny and sameorigin, which will block any framing, or framing by sites with a different origin, respectively. For older browsers, JavaScript framebusting techniques can be used but may not be effective in all browsers.
A code injection attack occurs when an input or otherwise external variable is used by an application unsanitized and causes modification to the application logic. This may allow an attacker to gain access to the application device or its data, cause denial of service, or a wide range of malicious side-effects.
The Authorization server and client MUST sanitize (and validate when possible) any value received, in particular, the value of the state and redirect_uri parameters.
The authorization server authorization endpoint and the client redirection endpoint can be improperly configured and operate as open redirectors. An open redirector is an endpoint using a parameter to automatically redirect a user-agent to the location specified by the parameter value without any validation.
Open redirectors can be used in phishing attacks, or by an attacker to get end-users to visit malicious sites by making the URI's authority look like a familiar and trusted destination. In addition, if the authorization server allows the client to register only part of the redirection URI, an attacker can use an open redirector operated by the client to construct a redirection URI that will pass the authorization server validation but will send the authorization code or access token to an endpoint under the control of the attacker.
This specification establishes the OAuth access token type registry.
Access token types are registered with a Specification Required ([RFC5226]) after a two week review period on the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Expert(s) may approve registration once they are satisfied that such a specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and comment, with an appropriate subject (e.g., "Request for access token type: example"). [[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: oauth-ext-review. ]]
Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Expert(s), and should direct all requests for registration to the review mailing list.
This specification establishes the OAuth parameters registry.
Additional parameters for inclusion in the authorization endpoint request, the authorization endpoint response, the token endpoint request, or the token endpoint response are registered with a Specification Required ([RFC5226]) after a two week review period on the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Expert(s) may approve registration once they are satisfied that such a specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and comment, with an appropriate subject (e.g., "Request for parameter: example"). [[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: oauth-ext-review. ]]
Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Expert(s), and should direct all requests for registration to the review mailing list.
The OAuth Parameters Registry's initial contents are:
This specification establishes the OAuth authorization endpoint response type registry.
Additional response type for use with the authorization endpoint are registered with a Specification Required ([RFC5226]) after a two week review period on the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Expert(s) may approve registration once they are satisfied that such a specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and comment, with an appropriate subject (e.g., "Request for response type: example"). [[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: oauth-ext-review. ]]
Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Expert(s), and should direct all requests for registration to the review mailing list.
The OAuth Authorization Endpoint Response Type Registry's initial contents are:
This specification establishes the OAuth extensions error registry.
Additional error codes used together with other protocol extensions (i.e. extension grant types, access token types, or extension parameters) are registered with a Specification Required ([RFC5226]) after a two week review period on the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Expert(s) may approve registration once they are satisfied that such a specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and comment, with an appropriate subject (e.g., "Request for error code: example"). [[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: oauth-ext-review. ]]
Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Expert(s), and should direct all requests for registration to the review mailing list.
| [RFC5849] | Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849, April 2010. |
| [I-D.ietf-oauth-v2-bearer] | Jones, M, Hardt, D and D Recordon, "The OAuth 2.0 Authorization Protocol: Bearer Tokens", Internet-Draft draft-ietf-oauth-v2-bearer-19, April 2012. |
| [I-D.ietf-oauth-saml2-bearer] | Mortimore, C, "SAML 2.0 Bearer Assertion Profiles for OAuth 2.0", Internet-Draft draft-ietf-oauth-saml2-bearer-12, May 2012. |
| [I-D.ietf-oauth-v2-http-mac] | Hammer-Lahav, E, "HTTP Authentication: MAC Access Authentication", Internet-Draft draft-ietf-oauth-v2-http-mac-01, February 2012. |
| [I-D.ietf-oauth-v2-threatmodel] | McGloin, M, Hunt, P and T Lodderstedt, "OAuth 2.0 Threat Model and Security Considerations", Internet-Draft draft-ietf-oauth-v2-threatmodel-02, February 2012. |
| [I-D.ietf-httpbis-p7-auth] | Fielding, R, Lafon, Y and J Reschke, "HTTP/1.1, part 7: Authentication", Internet-Draft draft-ietf-httpbis-p7-auth-19, March 2012. |
| [I-D.draft-hardt-oauth-01] | Hardt, D, Tom, A, Eaton, B and Y Goland, "OAuth Web Resource Authorization Profiles", January 2010. |
This section provides Augmented Backus-Naur Form (ABNF) syntax descriptions for the elements defined in this specification using the notation of [RFC5234]. Elements are presented in the order first defined.
Some of the definitions that follow use the URI-reference definition from [RFC3986].
Some of the definitions that follow use these common definitions:
VSCHAR = %20-7E NQCHAR = %x21 / %x23-5B / %x5D-7E NQSCHAR = %x20-21 / %x23-5B / %x5D-7E
The client_id element is defined in Section 2.3.1:
client-id = *VSCHAR
(This matches the userid definition in the HTTP Basic Authentication Scheme [RFC2617].)
The client_secret element is defined in Section 2.3.1:
client-secret = *VSCHAR
(This matches the password definition in the HTTP Basic Authentication Scheme [RFC2617].)
The response_type element is defined in Section 3.1.1 and Section 8.4:
response-type = response-name *( SP response-name ) response-name = 1*response-char response-char = "_" / DIGIT / ALPHA
The scope element is defined in Section 3.3:
scope = scope-token *( SP scope-token ) scope-token = 1*NQCHAR
The state element is defined in Section 4.1.1, Section 4.1.2, Section 4.1.2.1, Section 4.2.1, Section 4.2.2, and Section 4.2.2.1:
state = 1*VSCHAR
The redirect_uri element is defined in Section 4.1.1, Section 4.1.3, and Section 4.2.1:
redirect-uri = URI-reference
The error element is defined in Section 4.1.2.1, Section 4.2.2.1, Section 5.2, Section 7.2, and Section 8.5:
error = 1*NQSCHAR
The error_description element is defined in Section 4.1.2.1, Section 4.2.2.1, Section 5.2, and Section 7.2:
error-description = 1*NQSCHAR
The error_uri element is defined in Section 4.1.2.1, Section 4.2.2.1, Section 5.2, and Section 7.2:
error-uri = URI-reference
The grant_type element is defined in Section 4.1.3, Section 4.3.2, Section 4.4.2, Section 6, and Section 4.5:
grant-type = grant-name / URI-reference grant-name = 1*name-char name-char = "-" / "." / "_" / DIGIT / ALPHA
The code element is defined in Section 4.1.3:
code = 1*VSCHAR
The access_token element is defined in Section 4.2.2 and Section 5.1:
access-token = 1*VSCHAR
The token_type element is defined in Section 4.2.2, Section 5.1, and Section 8.1:
token-type = type-name / URI-reference type-name = 1*name-char name-char = "-" / "." / "_" / DIGIT / ALPHA
The expires_in element is defined in Section 4.2.2 and Section 5.1:
expires-in = 1*DIGIT
The username element is defined in Section 4.3.2:
username = *( %x20-39 / %x3B-7E )
(This allowed character set is VSCHAR excluding ":". This is compatible with the userid definition in the HTTP Basic Authentication Scheme [RFC2617].)
The password element is defined in Section 4.3.2:
password = *VSCHAR
(This matches the password definition in the HTTP Basic Authentication Scheme [RFC2617].)
The refresh_token element is defined in Section 5.1 and Section 6:
refresh-token = 1*VSCHAR
The syntax for new endpoint parameters is defined in Section 8.2:
param-name = 1*name-char name-char = "-" / "." / "_" / DIGIT / ALPHA
The initial OAuth 2.0 protocol specification was edited by David Recordon, based on two previous publications: the OAuth 1.0 community specification [RFC5849], and OAuth WRAP (OAuth Web Resource Authorization Profiles) [I-D.draft-hardt-oauth-01]. The Security Considerations section was drafted by Torsten Lodderstedt, Mark McGloin, Phil Hunt, and Anthony Nadalin. The ABNF section was drafted by Michael B. Jones.
The OAuth 1.0 community specification was edited by Eran Hammer and authored by Mark Atwood, Dirk Balfanz, Darren Bounds, Richard M. Conlan, Blaine Cook, Leah Culver, Breno de Medeiros, Brian Eaton, Kellan Elliott-McCrea, Larry Halff, Eran Hammer, Ben Laurie, Chris Messina, John Panzer, Sam Quigley, David Recordon, Eran Sandler, Jonathan Sergent, Todd Sieling, Brian Slesinsky, and Andy Smith.
The OAuth WRAP specification was edited by Dick Hardt and authored by Brian Eaton, Yaron Y. Goland, Dick Hardt, and Allen Tom.
This specification is the work of the OAuth Working Group which includes dozens of active and dedicated participants. In particular, the following individuals contributed ideas, feedback, and wording which shaped and formed the final specification:
Michael Adams, Amanda Anganes, Andrew Arnott, Dirk Balfanz, Aiden Bell, John Bradley, Brian Campbell, Scott Cantor, Marcos Caceres, Blaine Cook, Roger Crew, Brian Eaton, Wesley Eddy, Leah Culver, Bill de hOra, Andre DeMarre, Brian Eaton, Wolter Eldering, Brian Ellin, Igor Faynberg, George Fletcher, Tim Freeman, Luca Frosini, Evan Gilbert, Yaron Y. Goland, Brent Goldman, Kristoffer Gronowski, Justin Hart, Dick Hardt, Craig Heath, Phil Hunt, Michael B. Jones, Terry Jones, John Kemp, Mark Kent, Raffi Krikorian, Chasen Le Hara, Rasmus Lerdorf, Torsten Lodderstedt, Hui-Lan Lu, Casey Lucas, Paul Madsen, Alastair Mair, Eve Maler, James Manger, Mark McGloin, Laurence Miao, William Mills, Chuck Mortimore, Anthony Nadalin, Julian Reschke, Justin Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre, Marius Scurtescu, Naitik Shah, Luke Shepard, Vlad Skvortsov, Justin Smith, Haibin Song, Niv Steingarten, Christian Stubner, Jeremy Suriel, Paul Tarjan, Christopher Thomas, Henry S. Thompson, Allen Tom, Franklin Tse, Nick Walker, Shane Weeden, and Skylar Woodward.
This document was produced under the chairmanship of Blaine Cook, Peter Saint-Andre, Hannes Tschofenig, Barry Leiba, and Derek Atkins. The area directors included Lisa Dusseault, Peter Saint-Andre, and Stephen Farrell.
While many people contributed to this specification throughout its long journey, the editor would like to acknowledge and thank a few individuals for their outstanding and invaluable efforts leading up to the publication of this specification.
David Recordon for continuously being one of OAuth's most valuable assets, bringing pragmatism and urgency to the work, and helping shape it from its very beginning, as well as being one of the best collaborators I had the pleasure of working with.
James Manger for his creative ideas and always insightful feedback. Brian Campbell, Torsten Lodderstedt, Chuck Mortimore, Justin Richer, Marius Scurtescu, and Luke Shepard for their continued participation and valuable feedback.
Special thanks goes to Mike Curtis and Yahoo! for their unconditional support of this work for over three years.