C# ASP.Net MVC: RedirectFromLoginPage always goes to default url, and not to returnurl

Question

I have an MVC4 application with Membership logon (through FormsAuthentication).

This is defined in web.config as follows. My default url is home root (~/):

<roleManager enabled="true" />
<authentication mode="Forms">
  <forms defaultUrl="~" loginUrl="~/Account" />
</authentication>

In my AccountController in the Login post method, following code is relevant. This code is executed when the user clicks on the login with valid credentials.

if (Membership.ValidateUser(creds.Username, creds.Password))
{
    FormsAuthentication.RedirectFromLoginPage(creds.Username, false);
    return null;
}

Now, if I'm navigating (anonymously) to: ~/Admin, I get redirected to ~/Account to log in, which is perfect. I can see that the url is formed as follows:

http://localhost:23759/Account?ReturnUrl=%2fAdmin

But, when I succesfully login, I get redirected to home (~/) instead of ~/Admin

Please help! Many thanks!

Edit: Found the actual issue: it was the post method that wasn't receiving the querystring

Answer 1

I found the solution! Thanks to FlopScientist, who got me thinking further.

It was indeed because I was doing a POST method, which did not take the QueryString from the GET into account.

First I had this in my View:

@using (Html.BeginForm("Index", "Account")
{
    <div class="LoginBox">
    //Etc...
    </div>
}

I have updated it to following:

@using (Html.BeginForm("Index", "Account", new { ReturnUrl = Request.QueryString["ReturnUrl"] }, FormMethod.Post))
{
    //Etc...
}

Now I can actually see a querystring in my debug and I do get a correct redirect!