We didn't end up using the username from JupyterHub's Auth,
as it didn't add value but did add a corner case if the gitlab
authorization came back for a different user (such as if the user's
browser had logged into a different gitlab account in the meantime).

debug-gitlab was populating an empty username for consistency, but it
doesn't need to do that now.

Fix typos.

The debug-gitlab endpoint was extremely useful during
development, and may be useful for debugging of deployments
in the future.

Disable it by default.

Denton Gentry authored May 27, 2019 and Denton Gentry committed May 29, 2019

Login to discourse works when run as a JupyterHub managed service and
using gitlab.com as the authentication app.