Hello I use UAC module to register trunks to my providers. I've try to call to my provider. I send INVITE to my porvider and then It recieve me 407 reply "proxy authentication required".
Offcourse I can handle this reply manualy (by adding headers throuch header_add) and add md5 summ, but I think it`s not write and harder for Kamailio.
I find module or function at some module that  helps me send write INVITE with auth parameters as a reply ar 407 response of provider.

Thanks for help.