Allow any Domain to Log into Site

[dshanske]

This is a feature that would be useful for a future private/protected posts offering.

It would be something that could be disabled. Allow any URL to log in using the websignin form. If the site is not connected to an existing user, then create an unprivileged subscriber level user to represent it.

Request the new profile/email scope during the process, and these can be used to add context such as avatar, display name, and email to the user, otherwise if not offered, use the domain itself, or parse for h-card.

I'm not sure there is an issue with creating a theoretically unlimited amount of subscriber users.