Generates a timestamp in the proper DSA format.
Source
static String getTs() {
DateTime d = new DateTime.now();
if (d.millisecondsSinceEpoch == _lastTs) {
return _lastTsStr;
}
_lastTs = d.millisecondsSinceEpoch;
_lastTsStr = "${d.toIso8601String()}$TIME_ZONE";
return _lastTsStr;
}