问MVC - FormsAuthentication获取RoleName

EN

protected void Application_PostAuthenticateRequest(Object sender, EventArgs e)
{
    if (FormsAuthentication.CookiesSupported == true)
    {
        if (Request.Cookies[FormsAuthentication.FormsCookieName] != null)
        {
            try
            {
                //let us take out the username now                
                string username = FormsAuthentication.Decrypt(Request.Cookies[FormsAuthentication.FormsCookieName].Value).Name;
                string roles = string.Empty;

                using (userDbEntities entities = new userDbEntities())
                {
                    User user = entities.Users.SingleOrDefault(u => u.username == username);

                    roles = user.Roles;
                }
                //let us extract the roles from our own custom cookie


                //Let us set the Pricipal with our user specific details
                HttpContext.Current.User  = new System.Security.Principal.GenericPrincipal(
                  new System.Security.Principal.GenericIdentity(username, "Forms"), roles.Split(';'));
            }
            catch (Exception)
            {
                //somehting went wrong
            }
        }
    }
}

[Authorize]    
public ActionResult Index()
{
    bool isAdmin = System.Web.HttpContext.Current.User.IsInRole("admin");  // This also works correctly.
    Response.Write("role: " + isAdmin);

    string roleName = // The Code of How to get the actual Role Name
    Response.Write("roleName: " + roleName);  //e.g Admin, User...

    return View();
}