Abstract: A federated authentication service technology (10) for authenticating a subject (20) residing in a subject domain (12) on a network to a server application (38) residing in a server domain (18), wherein an authentication mechanism (32) residing in an authentication domain (16) affects the service provided by the server application (38). A client (22), which may be integrated non-human instances of the subject (20), authenticates the subject (20) and a protocol proxy (34) mediates with the authentication mechanism (32) to obtain a name assertion which the client can use to access the server application (38). When multiple authentication mechanisms (32) are available, an optional agent (24), mechanism resolution process (26) and mechanism repository (28), all residing in an agent domain (14), may be used to resolve to one suitable authentication mechanism (32).