SAML 2.0 concept that expands on the SAML 1.1 AuthenticationMethod attribute. Consists of an XML schema to express both technical and procedural aspects of user authentication and identity proofing. Very analagous to the oft-misunderstood concept of "level of assurance".

AuthnContexts can be grouped into "classes" that share common characteristics. An AuthnContext declaration can be thought of as an instance of one or more classes.

In SAML 2.0, requests for assertions, particularly AuthnRequests, can contain constraints on the allowable AuthnContexts that an !IdP should apply.