GitLab Agent Server Unauthorized error

/en/linux/blog/ kubernetesgitlabagentk

25/November/2025

authorRentaro

Without going into detail about how exactly and why everything is organized, access is provided through the following chain:

Nginx stream ingress <> Main Nginx Frontend <> Nginx Backend inside GitLab instance.

The Main Frontend manages the gitlab subdomain, which is closed to external access via auth_basic authorization.

Authorization on the /-/kubernetes-agent/ socket in gitlab itself occurs via a json/graphql payload.
But the Main Frontend also passes the state of the $remote_user field to the socket.
Accordingly, GitLab attempts to perform authorization based on Basic, but not on the parameters in the json/graphql payload itself.

And we get an error:

GitLab Agent Server: Unauthorized: Authorization header: expecting Bearer token

My biggest mistake

Of course, the second thing I did was disable authorization for my external IP address.
This was obvious since Authorization header: Bearer error was indicated.
But it didn’t work, I thought then.
After that there were a lot of deployments, reinitializations, configuration changes.
But even that didn’t work.

The devil is in the details

Inattention to obvious details led me a couple of days later to the Nginx log in the GitLab instance again.
In the log I noticed my login $remote_user from auth_basic passed from Frontend, which shouldn’t be there.

So what’s the mistake?

Let’s say you have auth_basic authorization enabled. The browser sends the Authorization: Basic header, since you entered your login and password to connect.
You disable authentication. Verify that it’s truly disabled, for example, using curl or wget.
However, when you refresh the page, or even open new tabs for this site, the browser continues to send the Authorization Header until you close and reopen it.
I just had to reopen the damn Fox!

Solution to the problem

location /-/kubernetes-agent/ {
            proxy_pass http://10.225.0.25:80;
            proxy_set_header Authorization    "";       # Wipe Authorization Header
            proxy_set_header X-Forwarded-User "";       # Also wipe any $remote_user
            proxy_set_header X-Remote-User    "";       # Any and all
            proxy_set_header Host             $host;
            proxy_set_header X-Forwarded-For  $proxy_add_x_forwarded_for;
            proxy_set_header X-Real-IP        $remote_addr;
            proxy_http_version 1.1;
            proxy_set_header Upgrade          $http_upgrade;
            proxy_set_header Connection       "upgrade";
}

Authorization is enabled, everything works correctly.

Original post on SecOps.it Blog • GitLab Agent Server Unauthorized error