Unfortunately we have had to remove Facebook authentication for our forums. Facebook has told us;
As a reminder, your app is currently in violation of Developer Policy 3.2:
“Only incentivize a person to log into your App, enter a promotion on your App’s Page, check-in at a place, or to use Messenger to communicate with your business. Don’t incentivize other actions.”
Unfortunately this means that all of the Badges that the forums use are in "violation" of this, so we've decided that the simpler option is to disable that integration. We'd like to apologise to the (relatively small number of) users that are logging in with their Facebook accounts that this will directly impact.
The Discourse team have a thread with more information here.