[Serusers] Authenticating INVITE requests method

Hello I am doing some security improvements to my configuration because I´ve realized that everyone can sends calls to PSTN gateways and other registered users even if the caller fails to register in SER, so now I instruct SER to check the username and password of the CALLER in every INVITE request like that: if (method=="INVITE") { if (!www_authorize("mydomain", "subscriber")) { www_challenge("mydomain", "0"); break; }; }; well it works but not when calls are generated in my gateway Cisco AS5350 (these GWs dont have register comand) so I need some advice to "exclude" gateway IP for this authorization process. thanks Rafael -- rrgv