Asserting Party (AP) -- This is an Authoritative identity provider (IDP) with the authority to make assertion statements about an Identity. Formally, the administrative domain that hosts one or more SAML authorities. Informally, an instance of a SAML authority.

Using SAML for SIP #

From (draft-tschofenig-sip-saml-04.txt) - The Authentication Service is the entity that authenticates and authorizes a user and creates an Assertion. This entity is the equivalent of the asserting party in the SAML terminology.