Methods, systems, and computer program products are disclosed that give entities flexibility to implement custom authentication methods of other entities for authentication of a principal in a federation by authenticating the principal by an identity provider according to a service provider's authentication policy and recording in session data of the identity provider an authentication credential satisfying the service provider's authentication policy. Authentication of a principal in a federation is also carried out by authenticating the principal by the identity provider according to an identity provider's authentication policy. Authentication of a principal in a federation is further carried out by receiving in the identity provider an authentication request from the service provider, the authentication request specifying the service provider's authentication policy.