Override the authentication class. This method needs to be overriden to
create a custom authentication backend. You must set the "auth_type" setting
in your hm3.ini file to "custom" to activate this class. More information
about the base class for authentication is located here:
This example extends the auth DB class, and simply defers the parent class
check_credentials( string $user, string $pass )
This is the method new auth mechs need to override.