[SR-Users] Presence request authentication

Hi, I have a complex setup consisting of two sip server, lets call them main server and presence server. The main server manages SIP register, calls, messages and so, however it does not support presence at all. It returns SIP response "405 Method Not Allowed" for any SIP PUBLISH, SUBSCRIBE or NOTIFY. The presence server is a Kamailio server, which unfortunately has no access to SIP subscriber database (so it can not do authentication), however it has access to User Location database. Now at presence server i want to put some kind of security for presence requests, since i can't do authentication, so i was thinking if i can verify if request has come from a location registered in location db. I found method "registered" in registrar module but unfortunately it checks if R-URI or any given URI is registered, while i want to do check against "received" address or contact address. Can you guys suggest any easy way to do it? I am thinking about using "reg_fetch_contacts" but not sure if it can serve the purpose. Thank you.