gitlab authentication using HTTP_REMOTE_USER environment variable

gitlab authentication using HTTP_REMOTE_USER environment variable

we have discovered gitlab, and I would like to integrate it in our global
authentication process, which relies on apache HTTP_REMOTE_USER
environment variable.
I have seen very little documentation on it, so I am looking desperately
for any help on how to do this. I would like to retrieve from the gitlab
application the HTTP_REMOTE_USER variable and use it to authenticate my
users.
I have tried to use omniauth and omniauth-ldap, but this returns only in
Errors 500 in my server and seems to be a little bit overkill to only
retrieve Apache HTTP_REMOTE_USER variable. What i am looking for is if
such a feature simply exists, or if i am going to a wrong direction; if
someone has some links to doc on it!
Many thanks