about formsAuthentication

hi,
i have created a custom principal class, and a custom Identity.
named SystemIdentity and SystemPrincipal.
SystemIdentity class has some additional properties ( UserID, UserName, Age, ...)
in my Global.asax file I changed PostAuthenticateRequest event as bottom
void MvcApplication_PostAuthenticateRequest(object sender, EventArgs e)
        {
            // Get the current user
            IPrincipal user = HttpContext.Current.User;

            // FormsAuthentication request
            if (user.Identity.IsAuthenticated && user.Identity.AuthenticationType == "F ...