Propagating QueryString parameter in RedirectToAction calls

public class PreserveQueryStringAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        var redirectResult = filterContext.Result as RedirectToRouteResult;
        if (redirectResult == null)
        {
            return;
        }

        var query = filterContext.HttpContext.Request.QueryString;
        // Remark: here you could decide if you want to propagate all
        // query string values or a particular one. In my example I am
        // propagating all query string values that are not already part of
        // the route values
        foreach (string key in query.Keys)
        {
            if (!redirectResult.RouteValues.ContainsKey(key))
            {
                redirectResult.RouteValues.Add(key, query[key]);
            }
        }
    }
}

and then:

[HttpPost]
[PreserveQueryString]
public ActionResult First() 
{
    ////////////////////
    // Lots of code ...
    ////////////////////

    return RedirectToAction("Second");
}