private static function _payloadMatches($signature, $payload)
 {
     $payloadSignature = Digest::hexDigestSha1(Configuration::privateKey(), $payload);
     return Digest::secureCompare($signature, $payloadSignature);
 }
 public static function sampleNotification($kind, $id)
 {
     $payload = base64_encode(self::_sampleXml($kind, $id)) . "\n";
     $signature = Configuration::publicKey() . "|" . Digest::hexDigestSha1(Configuration::privateKey(), $payload);
     return ['bt_signature' => $signature, 'bt_payload' => $payload];
 }