public function getSignedRequest() {
    if (!$this->signedRequest) {
      if (!empty($_REQUEST['signed_request'])) {
        $this->signedRequest = $this->parseSignedRequest(
          $_REQUEST['signed_request']);
      } else if (!empty($_COOKIE[$this->getSignedRequestCookieName()])) {
        $this->signedRequest = $this->parseSignedRequest(
          $_COOKIE[$this->getSignedRequestCookieName()]);
      }
    }
    return $this->signedRequest;
  }