[SR-Users] How to proxy/authenticate on third party sip server?

Can anybody help me with configuration kamailio to authenticate call on 3rd party server? I want to authenticate(and proxy) call's on other server. for example, user A have account on my server(let it be A(a)myserver.com) and account on other server (let it be AA(a)hisserver.com) myserver.com keeps A's credentials for AA(a)hisserver.com when A is registered on myserver.com, he make call to B(a)othersip.com (using myserver.com as a proxy) Kamailio on myserver authenticate itself on hisserver as AA(a)hisserver.com, makes call to destination, and connect it to A. How can I setup kamailio for such behavior? Which module should I use? UAC seems can authenticate on another server, but I don't sure that it do what I want. (I've tried it, but without much success)