Facebook login suddenly not working anymore

I haven’t searched the forums in depth, but it would be nice to know: can you setup multiple login authentication methods for a single user? If so, would the alternate login methods also have to be OAuth/SSO-based? …or could an alternate method be email and password?

Edit: nevermind, found the answer (which I believe is YES) [Resolved] Social Media OAuth As Email Validator, Regardless of Initial OAuth