This plugin allows you to use a basic OAuth2 provider as authentication for Discourse. It should work with many providers, with the caveat that they must provide a JSON endpoint for retriving information about the user you are logging in. This is mainly useful for people who are using login providers that aren't very popular. If you want to use Google, Facebook or Twitter, those are included out of the box and you don't need this plugin. You can also look for other login providers in our Github Repo.