Overview#Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants is described in RFC 7521 assertion is a package of information that facilitates the sharing of identity and security information across Security Domains. RFC 7521 Section 3 provides a more detailed description of the concept of an assertion.
OAuth 2.0 RFC 6749 is an authorization framework that enables a third-party application to obtain limited delegation access to a protected HTTP resource. In OAuth, those third-party applications are called clients; they access protected resources by presenting an Access Token to the HTTP Resource Server. Access Tokens are issued to clients by an Authorization Server with the (sometimes implicit) approval of the Resource Owner. These Access Tokens are typically obtained by exchanging an Authorization Grant, which represents the authorization granted by the Resource Owner (or by a privileged administrator).
Several Authorization Grant Types are defined to support a wide range of client types and user experiences. OAuth also provides an extensibility mechanism for defining additional grant types, which can serve as a bridge between OAuth and other protocol frameworks.
This specification provides a general framework for the use of assertions as Authorization Grants with OAuth 2.0. It also provides a framework for assertions to be used for client authentication. It provides generic mechanisms for transporting assertions during interactions with an Authorization Server's token endpoint as well as general rules for the content and processing of those assertions. The intent is to provide an alternative client authentication mechanism (one that doesn't send client secrets) and to facilitate the use of OAuth 2.0 in client-server integration scenarios, where the end user may not be present.
This specification only defines abstract message flows and processing rules. In order to be implementable, companion specifications are necessary to provide the corresponding concrete instantiations.
- "Security Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0 Client Authentication and Authorization Grants (RFC 7522) defines a concrete instantiation for Security Assertion Markup Language (SAML) 2.0 Assertions
- "JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants" RFC 7523 defines a concrete instantiation for JWTs.
Note: The use of assertions for client authentication is orthogonal to and separable from using assertions as an Authorization Grant. They can be used either in combination or separately. Client assertion authentication is nothing more than an alternative way for a Client to authenticate to the token_endpoint and MUST be used in conjunction with some Grant Type to form a complete and meaningful protocol request. Assertion Authorization Grants may be used with or without Client authentication or identification. Whether or not Client authentication is needed in conjunction with an assertion Authorization Grant, as well as the supported types of Client authentication, are policy decisions at the discretion of the Authorization Server.