Add Phabricator OAuth2 support
Allow for Phabricator's OAuth2 provider as an auth source.
Currently, the Team Edition only supports GitLab as an auth source, and this is a bit limiting, as some organisations such as mine need a bit more than what GitLab offers and have based their development processes on Phabricator.
We have an internal project ongoing to migrate from our private IRC server for communication to Mattermost or similar. Currently, MM is by far the most interesting solution out there, but the lack of more extensible/less tied to GitLab OAuth2 support is probably becoming a blocker.
We could probably feed the necessary patches to make Phab OAuth2 available to Mattermost, but first we'd like to know if this would be something that would be desired and accepted.
S Hollander commented
I have a similar need for a different OAuth2 provider. We currently use Gitea which is a really nice and simple Git web server. They recently added OAuth2 provider support (https://docs.gitea.io/en-us/oauth2-provider/) and it would be really nice if Mattermost would support it.