Agreed, even though I don't care for exposing the database quite this directly, it is a very interesting approach...
I'm also unsure of using the DB's authentication system. While approachable, I'm at a place where imho, for most systems there is a conflation of users, accounts, and logins. IMHO, a user may only have a single account, but a modern system should support multiple logins... Supporting social/jwt/oauth style logins in addition to local database backed logins is generally the best option for public facing sites/applications.. and even then jwt/oauth will allow for more seamless integration with internal SSO options.
Then again, this type of approach may work well if you want to be able to use it as an additional abstraction of your database access from a UI backing API.