protected function checkState(Request $request, $redirectUri)
{
// state is required and in valid format.
$state = $request->query->get('state');
$errors = $this->validator->validate($state, [new NotBlank(), new State()]);
if (count($errors) > 0) {
throw new InvalidRequestException(['redirect_uri' => $redirectUri, 'error_description' => 'The request includes an invalid parameter value']);
}
return $state;
}