IBS Portal真是经典的范例，实在值得好好研究。看看这两个Method：

        //*********************************************************************
        //
        // PortalSecurity.IsInRole() Method
        //
        // The IsInRole method enables developers to easily check the role
        // status of the current browser client.
        //
        //*********************************************************************
        public static bool IsInRole(String role) {
            return HttpContext.Current.User.IsInRole(role);
        }
        //*********************************************************************
        //
        // PortalSecurity.IsInRoles() Method
        //
        // The IsInRoles method enables developers to easily check the role
        // status of the current browser client against an array of roles
        //
        //*********************************************************************
        public static bool IsInRoles(String roles) {
            HttpContext context = HttpContext.Current;
            foreach (String role in roles.Split( new char[] {';'} )) {
            
                if (role != "" && role != null && ((role == "All Users") || (context.User.IsInRole(role)))) {
                    return true;
                }
            }
            return false;
        }