if (ref($username) and UNIVERSAL::isa($username,'Authen::SASL')) {
  $sasl = $username;
  $sasl->mechanism($mechanisms);
} 
else {
  die "auth(username, password)" if not length $username;
  $sasl = Authen::SASL->new(mechanism=> $mechanisms,
	callback => { user => $username,
        pass => $password,
        authname => $username,
        });
}