openID Connect dosen't require a user portion of the identifier to be
discovered and supports a opaque or pseudonymous user_id.
email is an optional attribute that can be returned by user consent.
OpenID 2.0 actively discouraged using email addresses for privacy reasons.
Teaching people to
It's important to remember that these identifiers need to be handled,
seen, and remembered by people. Especially in the long-tail case (which
is to say, IdPs who aren't big enough to get a log in button), users
will need to enter a piece of text into a website to tell the website
who they are.
Allowing user based discovery is not mutually exclusive with things that
provide browser based help for selecting a IdP.
Forcing a user to type a email address for twitter may also prove unnatural.
More help for the user by their trusted user agent is probably the better way
to go in the long
