AuthnContextDeclRef

AuthnContextDeclRef is an XML element used within Security Assertion Markup Language (SAML) assertions. SAML is an XML-based standard for exchanging authentication and authorization data between parties, specifically between an identity provider and a service provider. The AuthnContextDeclRef element is employed to provide a reference to an external document that defines the authentication context used for an assertion.

When an identity provider authenticates a user, it can convey details about that authentication process within a SAML assertion. The authentication context describes the specific conditions under which the authentication occurred. This could include information about the authentication method used (e.g., password, multi-factor authentication, biometrics), the time of authentication, and the assurance level.

The AuthnContextDeclRef element does not contain the definition of the authentication context itself. Instead, it points to a URI (Uniform Resource Identifier) where this definition can be found. This allows for a flexible and extensible way to describe authentication contexts without embedding complex definitions directly within the SAML assertion. Service providers can then retrieve and interpret this external definition to understand the security guarantees associated with the authentication. This separation of definition from assertion promotes interoperability and allows for the evolution of authentication methods.