An authentication server (e.g., AAA server) is described herein which is located in a CDMA2000 network and used to authenticate a user terminal that is connected to a non-CDMA2000 network. The authentication server receives an access request for authenticating the user terminal connected to the non-CDMA2000 network. Then, it obtains a root secret key shared between the user terminal and the CDMA2000 network and generates a GSM or UMTS-like authentication vector which is used to authenticate the user terminal according to a GSM or UMTS-like authentication method. The access of the terminal to the non-CDMA2000 network is granted upon successful authentication. According to embodiments of the invention, the non-CDMA2000 network can be a WLAN network, and the authentication methods used can be EAP SIP or EAP AKA. The present invention allows one to use authentication servers that were originally intended for WLAN-3GPP interworking scenarios also in WLAN-CDMA2000 network interworking.