There’s no convenience method for no-content result because, by default, when a action returns void, the response will have the HTTP status 204.
If you wish to explicitly indicate that on the action, you could also return a StatusCode(HttpStatusCode.NoContent) from your action or a
ResponseMessage(new HttpResponseMessage(HttpStatusCode.NoContent)).
The Unauthorized() convenience method gives you a 401 status so, for Forbidden (403), you would also have to use StatusCode(HttpStatusCode.Forbidden) or
ResponseMessage(new HttpResponseMessage(HttpStatusCode.Forbidden))