def on_post(self, req, resp):
        """A datetime adder endpoint."""
        args = req.context["args"]
        value = args["value"] or dt.datetime.utcnow()
        if args["unit"] == "minutes":
            delta = dt.timedelta(minutes=args["addend"])
        else:
            delta = dt.timedelta(days=args["addend"])
        result = value + delta
        req.context["result"] = {"result": result.isoformat()}
A datetime adder endpoint.