Update: the below error has been resolved. Please reference this comment if you are still encountering errors:
This should be fixed and everything working normally. Could you please let us know if you still see problems?
That said, if you opened your app in the editor, you might have ended up with a version that has an error. Please reopen in the editor to get to a good version. Or revert to a previous stable version.
We recently deployed a change containing a bug that prevents applications which use domain authentication from loading. We are rolling back this change now. We expect access to the affected applications to be restored in the next 15-30 minutes. We will post a public incident report below once we have completed our internal investigation.
We apologize for the impact that this bug has caused.