private String buildPayload(WebhookNotification.Kind kind, String id) {
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
String timestamp = dateFormat.format(new Date());
String payload =
"<notification><timestamp type=\"datetime\">"
+ timestamp
+ "</timestamp><kind>"
+ kind
+ "</kind><subject>"
+ subjectXml(kind, id)
+ "</subject></notification>";
return Base64.encodeBase64String(payload.getBytes()).trim();
}