1. In a system comprising a user equipment (UE), a service provider (SP), and an authentication end point (AEP) which communicate via a network, a method of authenticating the UE by the AEP, comprising, at the AEP: determining one or more authentication protocols or credentials that may be used to authenticate the UE; negotiating with the UE to select one of the authentication protocols or credentials that are acceptable to the SP; and authenticating the UE using the selected authentication protocol or credentials.