Yes. You will achieve that by inheriting from the base TUser entity class and adding your own properties.
Yes.
You will have a Sphinx server (TSphinxServer component) which is a XData server that provides all functionality for the authentication. Under the hood such server saves information (like users) directly in a database, using Aurelius.
Thus, yes, authentication server is XData, and database can be any Aurelius-compatible database.
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