Change GitLab instance used for authentication

Hello everyone,

We are currently using the Mattermost Team edition and are using our own Enterprise GitLab instance as authentication.
We want to set up a Community GitLab instance to use as authentication instead, since otherwise everyone who wants to use Mattermost has to have a Enterprise GitLab Account.

Is it possible to just switch the authentication on Mattermost to a different GitLab instance while maintaining user history and teams for already registered users?

Would be glad if anyone knew anything before we tried it for nothing.

~ onno_ole ~

We just tried to do exactly this switch from one Gitlab instance to another. After setting everything up as documented on the new instance, we changed the authentication credentials on MM to the new appId and appSecret.
The result was this error An error has occurred ***Client authentication failed due to unknown client, no client authentication included, or unsupported authentication method.***

This locked us out entirely, as no one was able to login to MM with the only allowed method (Gitlab) and we were required to manually revert the changes in the MM config database to connect back to the previous Gitlab instance.

Obviously, there is something else kept around here except for the app credentials that is causing a mismatch and prevents the user from authentication. I have yet to find out what that is.

Any ideas or suggestions how to solve this would be extremely appreciated and directly impacting your karma balance.