title: How do I get the current Url from within a FilterAttribute?
body: <p>I am writing an Authorize filter attribute adn I'm having trouble figuring out how to get the current url as a string so I can pass it as a parameter to the LogOn action. The goal is that if a user successfully logs on, they will be redirected to the page they were originally trying to access.</p>
  
  <pre><code>public override void OnAuthorization(AuthorizeContext filterContext)
  {
      base.OnAuthorization(filterContext);
  
      ... my auth code ...
      bool isAuth ;
      ... my auth code ...
  
      if(!isAuth)
      {
          filterContext.Result = new RedirectToRouteResult(
              new RouteValueDictionary { 
                  { "Area", "" }, 
                  { "Controller", "Account" }, 
                  { "Action", "LogOn" },
                  { "RedirectUrl", "/Url/String/For/Currnt/Request" } // how do I get this?
              }
          );
      }
  }
  </code></pre>
  
  <p>How do I get the full string Url from the current request?</p>