Mattermost signup failure. Can run mattermost but can not create groups

When I click the Create Group from the, I get this error on screen:
An error has occurred
Client authentication failed due to unknown client, no client authentication included, or unsupported authentication method.

NO errors in log with gitlab-ctl tail, and from those logs I see it executes the following post:…&…%3D

I don’t see anything in the log that fails, but it seems internally to be doing some OATH token stuff:

==> /var/log/gitlab/gitlab-rails/production.log <==
Started GET “/oauth/authorize?response_type=code&client_id=…&…%3D” for at 2016-05-12 10:52:41 -0500
Processing by Oauth::AuthorizationsController#new as HTML
Parameters: {“response_type”=>“code”, “client_id”=>"…", “redirect_uri”=>“”, “state”=>“eyJ…=”}
Started POST “/ci/api/v1/builds/register.json” for at 2016-05-12 10:52:41 -0500

All HTTP responses seem to be 200 OK.


Turns out the documentation is pretty clear here.

  1. Go to and create an Application.
  2. Use the following pair of URIs, but change the url to your mattermost:
3. Take the app ID and token values you are given and put them in the right place in /etc/gitlab/gitlab.rb
3. gitlab-ctl reconfigure