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

When I click the Create Group from the mattermost.mycompany.biz, 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:

https://gitlab.mycompany.biz/oauth/authorize?response_type=code&client_id=fe…&redirect_uri=http%3A%2F%2Fmattermost.mycompany.biz%2Fsignup%2Fgitlab%2Fcomplete&state=eyJ…%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=…&redirect_uri=http%3A%2F%2Fgitlabchat.ramsoft.biz%2Fsignup%2Fgitlab%2Fcomplete&state=e…%3D” for 127.0.0.1 at 2016-05-12 10:52:41 -0500
Processing by Oauth::AuthorizationsController#new as HTML
Parameters: {“response_type”=>“code”, “client_id”=>"…", “redirect_uri”=>“http://gitlabchat.ramsoft.biz/signup/gitlab/complete”, “state”=>“eyJ…=”}
Started POST “/ci/api/v1/builds/register.json” for 127.0.0.1 at 2016-05-12 10:52:41 -0500

All HTTP responses seem to be 200 OK.

Warren

Turns out the documentation is pretty clear here.

  1. Go to https://gitlab.yourcompany.biz/admin/applications and create an Application.
  2. Use the following pair of URIs, but change the url to your mattermost:
    http://mattermost.yourcompany.biz/signup/gitlab/complete

http://mattermost.yourcompany.biz/login/gitlab/complete
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