Log in to gitlab using Basic auth

Hello everyone,

I currently have a working gitlab community edition installation (omnibus packages) on CentOS 7.
I have a working ldap link where using sign in using userPricipalName (user@domain).

I read that basic auth is supported in some way or another, but I’m not sure how/how to configure this.

My (load balancer/reverse proxy) sends the users credentials (userPricipalName) to the gitlab server already in the header (basic auth).
How to I use this to log my users into gitlab automatically on the front end? (/gitlab/users/sign_in)