How can I preserve the url (with the querystring) after an Http Post but also add an error to the Model State?

Question

Essentially want I'm trying to do is authenticate a user by having them enter their account and their social security number. If they enter an incorrect combination, I do the following on the Authenticate post action:

ModelState.AddModelError("Authenticated", authenticationError);
return View();

This displays the error, but then I lose what was in my query string. An alternative to keep the query string is:

ModelState.AddModelError("Authenticated", authenticationError);
return Redirect(Request.Url + "?returnUrl=" + returnUrl);

This will keep the query string, but the error will not display. I assume this is because the ModelState has changed.

I need the returnUrl because the user is forced to the Authenticate page whenever they click to view a specific event. I want to set it up so that they still go to this event once they authenticate themselves.

Is there a way I can achieve both the preservation of the query string and display the model error?

Answer 1

Ivan Korytin's answer was the best (and only answer I could find which seemed to actually work properly without using hidden field hacks) which I've improved a little with Request.QueryString.

You have to put the parameters as part of the form action:

<form action="@Url.Action("CreateEntity", "Employee")?@(Request.QueryString)"
  enctype="multipart/form-data" method="POST">

When you perform the following the query string (and GET parameters) are now preserved:

[HttpPost]
public ActionResult MyAction(MyAction model)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }