How to add two different login url in form based authentication in C# MVC4?

We can not set two login urls for login inside webconfig file.If we create our own custom Membership provider, we have to set it as defaultprovider for making the [Authorize] attribute workable for it. But in my case, there were two providers. Both are custom providers, and I wasn't allowed to change the default provider. One provider is used for Admin login(the default provider), another provider used for user login (custom provider). In web config form authentication was enabled

<authentication mode="Forms">
  <forms loginUrl="~/Account/Login" timeout="2880" />
</authentication>

So, when I was using [Authorize] attribute, it was taking me to the admin login page and it is expected. But I needed an attribute which would take me to user login page. So I created a [AuthorizeUser] attribute which is now taking users to user login section.

public class AuthorizeUserAttribute : AuthorizeAttribute
{

    protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
    {
        var username = filterContext.HttpContext.User.Identity.Name;
        if (username != "")
        {
            base.HandleUnauthorizedRequest(filterContext);
        }
        else
        {
            filterContext.Result = new RedirectToRouteResult(new
            RouteValueDictionary(new { controller = "Login", action = "Index" }));
        }
    }
}

This attribute is taking my users into user login page at ~/login