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.