C# get Session-Value in .net MVC-RouteHandler

I would create a dynamic routing in my ASP.Net – MVC Project (Framework 4.5.1). To do this I create a custom MvcRouteHandler which work fine until I tried to add a new condition in base of a User-Session-Value. Unfortunately I’ve noticed, that the Sessions in the Routing-Class always are null. Is there any way to get the Session-Value already in the Routing-Handler – or is that another way to store User-related Data which I can access in the Routehandler too?

Here's my Code - Routeconfig.cs:

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{*FriendlyUrl}"
        ).RouteHandler = new myRouteHandler();
    }

...and (the simplified) myRouteHandler.cs:

public class myRouteHandler : MvcRouteHandler, IRequiresSessionState
{
    protected override IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        String myController = "Home";
        String myAction = "Index";
        Int32 myRouteId = 0;

        //here i would try to get a Session-Value, but Session is always null...
        var mySession = requestContext.HttpContext.Session["mySession"];

        if (mySession != null)
        {
            //do something different e.g.
            myAction = "About";
        }

        requestContext.RouteData.Values["controller"] = myController;
        requestContext.RouteData.Values["action"] = myAction;
        requestContext.RouteData.Values["id"] = myRouteId;

        return base.GetHttpHandler(requestContext);
    }
}