Set Default Route for a Controller as Index View - asp.net-mvc

Question

So I have the url:
www.mywebsite/signup/index
That works fine.
What I want to do is add a new route mapping to the RouteConfig class that allows the following url to work:
www.mywebsite/signup
I have tried:
routes.MapRoute(
name: "Signup",
url: "{controller}/",
defaults: new { controller = "Signup", action = "Index", id = UrlParameter.Optional }
And:
routes.MapRoute(
name: "Signup",
url: "{controller}",
defaults: new { controller = "Signup", action = "Index", id = UrlParameter.Optional }
And:
routes.MapRoute(
name: "Signup",
url: "{controller}/*",
defaults: new { controller = "Signup", action = "Index", id = UrlParameter.Optional }
My RouteConfig class has been customized and the default routing when creating a new ASP.NET MVC Project has been changed, it currently looks like this:
routes.MapRoute(
name: "DefaultConstrained",
url: "{controller}/{action}/{id}",
defaults: new { action = "Index", controller = "Home", id = UrlParameter.Optional },
constraints: new { controller = ConstrollersAsCSV() }
);
routes.MapRoute(
name: "SiteLogin",
url: "{site}",
defaults: new { controller = "User", action = "Login", site = "" },
constraints: new { site = new ExcludeAndUseRegex() }
);
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "User", action = "Login", id = UrlParameter.Optional }
);
Where the constraint method ConstrollersAsCSV (which I don't know what that is doing) is:
public static string ConstrollersAsCSV(string optional = null)
{
var list = GetControllerNames();
var sb = new StringBuilder();
sb.Append("(");
if (!string.IsNullOrWhiteSpace(optional))
sb.Append(optional);
foreach (var cont in list)
{
if (sb.Length > 1)
sb.Append("|");
sb.Append(cont.Replace("Controller", ""));
}
sb.Append(")");
return sb.ToString();
}
And the implementation of GetControllerNames is:
public static List<string> GetControllerNames()
{
List<string> controllerNames = new List<string>();
GetSubClasses<Controller>().ForEach(
type => controllerNames.Add(type.Name.ToLower()));
GetSubClasses<ApiController>().ForEach(
type => controllerNames.Add(type.Name.ToLower()));
controllerNames.Add("elmah");
return controllerNames;
}
And the implementation of GetSubClasses is:
private static List<Type> GetSubClasses<T>()
{
return Assembly.GetCallingAssembly().GetTypes().Where(
type => type.IsSubclassOf(typeof(T))).ToList();
}
The error I am getting when going to www.mywebsite.com/signup is:
**HTTP Error 403.14 - Forbidden**