Multi-RAT UEs currently have 2 independent paths to authenticate with HSS (either via the MME or the 3GPP AAA Server causing repeated authentication messages to HSS. The use of one unified authentication path between the UE and HSS for Small Cell and Wi-Fi authentication is described. First, a new 3GPP EPC-TWAN interworking architecture has the MME manage all the authentication requests from multi-RAT UEs. Second, new unified authentication procedures are added, which allow the ISWN-based multi-RAT UE to be authenticated directly with the HSS, irrespective of its current access network (TWAN or HeNB). Third, new fast re-authentication procedures for Inter-RAT handover scenarios are done. Finally, the needed extensions to the various standard protocol messages to execute the authentication procedures are described.