A method of establishing a multicast and broadcast session for a multicast and broadcast multimedia subsystem, MBMS, service for providing content to a plurality of User Equipments, UEs, using at least one of a multicast and a broadcast data transmission, the method performed by a core network, CN , of a communication system, wherein the CN comprises an authentication server function, AUSF, , a unified data management, UDM, function , an access and mobility function, AMF and a Session Management Function, SMF , the method comprising: receiving , by the SMF, of the core network, CN , a session establishment request sent by a UE to establish the session to provide the content directed to the plurality of UEs ; transmitting , by the SMF , an authorization request based on said session establishment request for session subscription information to the UDM function of the CN , and authorizing , by the UDM function the session based on communication with a membership function (541a; 741); and receiving , by the SMF , an authorization response for authorization of the session sent by the UDM function ; wherein, when a decryption code to decrypt the provided content for the session has been stored in the SMF , the method comprises transmitting, by the SMF , based on the authorization response the decryption code towards the UE ; and when a decryption code for the session is not stored in the SMF , the method comprises: transmitting , by the SMF , based on the authorization response to the AUSF a code request for the decryption code; and transmitting , by the AUSF , the decryption code to the UE via the AMF or via a combination of the AMF and the SMF ; wherein the method further comprises obtaining, by the AUSF the decryption code based on a multicast and broadcast, MB, session security information exchange with a MBMS security function, SF , wherein the MBMS SF is integrated with the AUSF . receiving , by the SMF, of the core network, CN , a session establishment request sent by a UE to establish the session to provide the content directed to the plurality of UEs ; transmitting , by the SMF , an authorization request based on said session establishment request for session subscription information to the UDM function of the CN , and authorizing , by the UDM function the session based on communication with a membership function (541a; 741); and receiving , by the SMF , an authorization response for authorization of the session sent by the UDM function ; wherein, when a decryption code to decrypt the provided content for the session has been stored in the SMF , the method comprises transmitting, by the SMF , based on the authorization response the decryption code towards the UE ; and when a decryption code for the session is not stored in the SMF , the method comprises: transmitting , by the SMF , based on the authorization response to the AUSF a code request for the decryption code; and transmitting , by the AUSF , the decryption code to the UE via the AMF or via a combination of the AMF and the SMF ; wherein the method further comprises obtaining, by the AUSF the decryption code based on a multicast and broadcast, MB, session security information exchange with a MBMS security function, SF , wherein the MBMS SF is integrated with the AUSF . transmitting , by the SMF , based on the authorization response to the AUSF a code request for the decryption code; and transmitting , by the AUSF , the decryption code to the UE via the AMF or via a combination of the AMF and the SMF ; wherein the method further comprises obtaining, by the AUSF the decryption code based on a multicast and broadcast, MB, session security information exchange with a MBMS security function, SF , wherein the MBMS SF is integrated with the AUSF . <EOS>