The proper thing to do is to create a custom
Zend_Auth_Adapter that authentication to your particular DB schema.
Its actually pretty easy, there is only a single method in the interface to implemnt. Its also possible you could jsut extend
Zend_Auth_Db_Adapter and override methods as necessary. Probably only what builds executes and returns the query result. But honestly i would just implment the interfae from scratch were it me. A lot easier that way IMO :-)