The proposed technology generally relates to interworking and integration of different radio access networks, and more specifically to carrier aggregation between different radio access networks such as a cellular radio access network, e.g. a 3GPP network, on one hand and a WLAN network such as Wi-Fi, on the other hand. Such tight interworking/aggregation of radio access networks puts new requirements on efficient handling of authentication and security aspects. The proposed technology provides methods, and corresponding network nodes, computer programs, carriers comprising such computer programs, and computer program products as well as arrangements to support carrier aggregation between different radio access networks.