Hello, Raúl!
OK, do you ever hear about AUTH_RADIUS ? :-)
Yes, we know, at the end it's other DB ;-)
OK. Can you imagine auth_http in place of auth_radius or auth_diameter ? I don't think that http with some encapsulated text data is worth then than RADIUS. But I think auth_http is bad idea. db_rest + auth_db is better.
We can make all db-aware modules work with this "database".