401 code not handled in mvc project properly - asp.net-mvc-4

Question

I have ASP.NET MVC4 project with custom AuthorizeAttribute to control the authorization. In order to explain my situation easier I created a dummy project to illustrate the issue.
I have one single controller
using System.Web.Mvc;
using MvcApplication2.Helper;
using MvcApplication2.Models;
namespace MvcApplication2.Controllers
{
public class HomeController : Controller
{
public ActionResult Index()
{
var model = new ViewModel();
return View(model);
}
[HttpPost]
public ActionResult Index(ViewModel model)
{
Session["ModelValue"] = model.InputValue;
return RedirectToAction("Step2");
}
[MyAuthorize]
public ActionResult Step2()
{
return View();
}
}
}
The purpose is very simple, From Index I accept some input, store the value in a session and redirect to Step2. I have my authorize attribute on step 2. The code for my attribute is
using System;
using System.Web;
using System.Web.Mvc;
namespace MvcApplication2.Helper
{
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true)]
public class MyAuthorizeAttribute : AuthorizeAttribute
{
protected override bool AuthorizeCore(HttpContextBase httpContext)
{
if (httpContext.Session["ModelValue"] == null)
{
return false;
}
else
{
string inputValue = httpContext.Session["ModelValue"] as string;
if (inputValue != "1")
{
return false;
}
else
{
return true;
}
}
}
}
}
The purpose is very simple, check if the session value is 1 or not.
Run the application, you input 1 in textbox and you see step2 view, if you input anything else you get the default 401.0 page.
Now I opened the web.config file to include
<system.web>
<customErrors mode="On" defaultRedirect="~/Error">
<error statusCode="401" redirect="~/401.htm" />
</customErrors>
<compilation debug="true" targetFramework="4.0" />
</system.web>
I hope when the application captures 401 code, I should see the content of 401.htm. But the reality is that I still get the default 401 error display from server.
Any idea why?

Answer 1

In addition use this:
<system.webServer>
<httpErrors>
<error statusCode="401" path="~/Home/Login"/>
<error statusCode="404" path="~/Error/NotFound"/>
</httpErrors>
</system.webServer>