docs: protected void handlePasswordValidationCallback(PasswordValidationCallback callback) throws RemoteException, EntryNotFoundException, CustomRegistryException {
          Subject clientSubject = callback.getSubject();
          String userName = callback.getUsername();
          String password = new String(callback.getPassword());
          if (tc.isDebugEnabled()) {
              Tr.debug(tc, "handlePasswordValidationCallback", new Object[] { callback, userName });
          }
  
          if (clientSubject != null) {
              UserRegistry registry = getUserRegistry();
              if (registry != null) {
                  if (checkUserPassword(userName,
                                        password,
                                        registry,
                                        registry.getRealm(),
                                        clientSubject)) {
                      callback.setResult(true);
                  } else {
                      callback.setResult(false);
                  }
              }
          }
          if (tc.isDebugEnabled()) {
              Tr.debug(tc, "handlePasswordValidationCallback", "valid password? " + callback.getResult());
          }
      }