/**
  * Validate timestamp param
  * @param string $validsec
  */
 public function validateTimestamp($validsec)
 {
     if ($this->_timestamp > OAuth2Util::generateTimestamp() + (int) $validsec || $this->_timestamp < OAuth2Util::generateTimestamp() - (int) $validsec) {
         $this->_enabled = false;
         $this->_code = 'HTTP/1.1 400 Bad Request';
         $this->_error = 'invalid_timestamp';
     }
 }