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
CEO @ MICE