public function getAppData()
{
$app_data = isset($this->signed_request['app_data']) ? $this->signed_request['app_data'] : null;
if (is_string($app_data)) {
$data = json_decode($app_data, true);
if (json_last_error() == JSON_ERROR_NONE) {
$app_data = $data;
}
}
return $app_data;
}