OpenID Authentication broken

Troubleshooting
1

Hi all

I have a problem.

I deployed a mattermost free plan instance (last year). I configured Mattermost to obtain an OpenID Connect authentication to an “Authentik” server, and 90% of my users use this authentication method without error since 1 year.

Last week, just after a new user creation, and for ressources reasons, i rebooted my authentik server… And, since this reboot, i obtain this error on my Webpage Mattermost during authentication phase:

Error : 

There is already an account associated with that email address using a sign in method other than gitlab. Please sign in using gitlab.
  • I read mattermost logs and i have :
{"timestamp":"2025-09-17 16:01:48.052 Z","level":"warn","msg":"Error while creating session for user access token","caller":"app/session.go:114","error":"createSessionForUserAccessToken: Invalid or missing token., resource \"UserAccessToken\" not found, id: token="}
  • I checked the database and the field authservice in users table is still gitlab for all of my SSO accounts

I don’t understand, because all of the services like wiki, and others use the “Authentik” for authentication and they work fine. But Mattermost authentication seems to be broken.

To debug, Yesterday, i created a new user on my Authentik server, and i could by authenticated on Mattermost without issue…but i can’t with my older users…

Have you ever saw this problem, please ?