public static function getPublicCertificates() {
    $req = new GetPublicCertificateForAppRequest();
    $resp = new GetPublicCertificateForAppResponse();

    try {
      ApiProxy::makeSyncCall(self::PACKAGE_NAME, 'GetPublicCertificatesForApp',
          $req, $resp);
    } catch (ApplicationError $e) {
      throw self::applicationErrorToException($e);
    }

    $result = [];

    foreach ($resp->getPublicCertificateListList() as $cert) {
      $result[] = new PublicCertificate($cert->getKeyName(),
                                        $cert->getX509CertificatePem());
    }

    return $result;
  }