protected function _validateSslCertificate($validation_result)
  {
    if (in_array(
        $validation_result,
        [
          CURLE_SSL_CERTPROBLEM,
          CURLE_SSL_CACERT,
          CURLE_SSL_CACERT_BADFILE,
          CURLE_SSL_CRL_BADFILE,
          CURLE_SSL_ISSUER_ERROR
        ]
      )
    ) {
      throw new \Exception(
        'Error ' . $validation_result
        . ' while validating the Twitter API certificate.'
      );
    }
  }