System.ArgumentNullException: Value cannot be null. Parameter name: url

Question

In asp.net mvc application, i am trying to redirect to new route in Application_AuthenticateRequest.If the user is not authenticated, then i am redirecting to different url. Following is the code,

protected void Application_AuthenticateRequest(object sender, EventArgs e)
{
   var urlHelper = new UrlHelper(HttpContext.Current.Request.RequestContext);
   var loginUrl = urlHelper.Action("Login", "Default");
   Response.Redirect(loginUrl);
}

In this above code, urlHelper.Action method returns empty string even after route registration happens at Application_Start event.

Any idea to resolve this error?

Following is the RouteConfiguration in Application_Start,

        RouteTable.Routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { id = UrlParameter.Optional });