To me, that sounds like a useful shorthand. It would probably not at all be difficult to add support for that to the broker (apart from the usual wrestling with Rust), so yeah, why not. Though I maybe miss some implications for the RP – breaking the expectation that it is just an email is bad if you use the email as an email, and if you want to have the option to easily move away from portier.

The FB thing was more, iirc, that you don't want to enter an email and then get the FB dialogue just because you used your email on FB.