Gitlab web access - header based authentication

Hi all,
We have a fresh new gitlab installation for our platform that reside under an SSO with a webgate that resolve all access.
Therefore we need a simple header based authentication system that authenticate entering user simply by getting an http header containing the userid to authenticate.
We know the are a variety of external authentication plugins but none is so simple as requested.
Please help us discover that possibility or, in alternative, how to implement it.
Thanks in advance.
Emilio Dolce