private static function _matchingSignature($signaturePairs)
 {
     foreach ($signaturePairs as $pair) {
         $components = preg_split("/\\|/", $pair);
         if ($components[0] == Configuration::publicKey()) {
             return $components[1];
         }
     }
     return null;
 }
 public static function sampleNotification($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];
 }