void authenticate(UserRealm realm, HttpRequest request) {
   _userPrincipal = realm.authenticate(_jUserName, _jPassword, request);
   if (_userPrincipal != null) _realm = realm;
 }
 void authenticate(UserRealm realm, String user, String password, HttpRequest request) {
   _jUserName = user;
   _jPassword = password;
   _userPrincipal = realm.authenticate(user, password, request);
   if (_userPrincipal != null) _realm = realm;
 }