Hi!
Don’t know specifically about Gitlab but I had similar troubles integrating OAuth2 authentication with other applications. They demanded ID, email, etc. attributes to name.
These values are accessible from the <mailcow server>/oauth/profile response.
Example here:
{
"success": true,
"username": "email@example.com",
"identifier": "email@example.com",
"email": "email@example.com",
"full_name": "Example User",
"displayName": "Example User",
"created": "2020-05-15 11:33:08",
"modified": "2020-05-15 12:23:31",
"active": 1
}
Hope this helps a bit.