supabase auth stores your users in the same database created, just in a separate schema so you have full access to it to perform joins or enforce referential integrity.

Cool! Now I know at least two auth services that don't have this user storage problem.

FaunaDB also integrates DBaaS with their auth, but FaunaDB is a very different DB that doesn't work with standard SQL.

And FaunaDB doesn't have support for anonymous users!