Hello, I would appreciate any help you can provide on this matter, 

I would like to make an outgoing INVITE request which will have a digest authorization with password and username.
I was wandering around the Auth module to find the most fit method to build this header but hadn't found anything.

Maybe I am missing something really obvious here, thanks for the help in advance

Hi

uac_auth from the uac module is what you want. https://kamailio.org/docs/modules/5.6.x/modules/uac.html

-Barry