Looking for logging into the Gitlab Mattermost site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Gitlab Mattermost site. After that you can login as usual with your login credentials.
https://docs.gitlab.com/omnibus/gitlab-mattermost/
https://docs.mattermost.com/deployment/sso-gitlab.html
https://forum.mattermost.org/t/cannot-log-in-with-gitlab/5027
https://www.mattermost.org/about-gitlab-mattermost-com/
https://forum.mattermost.org/t/correct-login-page/1583
https://forum.mattermost.org/t/where-to-find-mattermost-after-installing-gitlab-omnibus/175
https://forum.mattermost.org/t/how-is-gitlab-sso-configured-in-gitlab-mattermost/147
https://forum.mattermost.org/t/using-gitlab-login-with-desktop-client/5596
https://forum.mattermost.org/t/impossible-to-log-in-using-v4-api/3606
https://github.com/mattermost/mattermost-server/issues/8636
https://stackoverflow.com/questions/35458595/how-to-use-gitlab-and-gitlab-mattermost-on-one-machine
https://github.com/mattermost/mattermost-mobile/issues/355
https://www.zdv.uni-mainz.de/gitlab/