$remote_user not available on the the directive

[minijusl]

There are couple issues/questions asking how to retrieve remote user in backend application and the correct answer is pass it down as a custom header via proxy to the backend application.

#14
https://stackoverflow.com/questions/70191631/how-to-get-username-after-successful-kerberos-authentication-using-nginx

I was trying to return $remote_user immediately in the same location directive's block. Unfortunately, it always returns empty value even the authentication itself is successful.

        location / {
          auth_gss on;
          auth_gss_keytab /usr/local/etc/krb5.keytab;
          auth_gss_allow_basic_fallback off;

          add_header Content-Type text/plain;
          return 200 'remote user: $remote_user';
        }

Same, behaviour is observed on access.log as well - $remote_user is always empty.

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;