title: Automatically provide HttpUnauthorizedResult (401 error) default StatusDescription instead of null
body: <p>In our ASP.NET MVC C# web application, we often want to return a generic Unauthorized message as a JSON response to AJAX calls if the user fails some kind of authentication check. My first thought was to do it this way:</p>
  
  <pre><code>return Json(new HttpUnauthorizedResult().StatusDescription);
  </code></pre>
  
  <p>The problem is, the <code>StatusDescription</code> property is <code>null</code> by default. It would be great if we could somehow overload the constructor to instantiate this property to have some generic unauthorized message if none is provided, but I can't figure out how to do it.</p>
  
  <p>Does anyone know how to implement this? Please also feel free to suggest a better way to implement Http error messages in AJAX calls if this is not a good method.</p>