custom authorize attribute

hi,
i am creating a custom authorizeAttribute drived from AuthorizeAttribute.
public class CustomAuthorizeAttribute : AuthorizeAttribute
    { }
and using this on action methods and classes.
i am not using the asp.net membership management. so i am not using roles from my roles table.
for example 
        [CustomAuthorize(Roles=????)]
        public ActionResult Index()
        {
            return View();
        }
in this stuation how can i take the roles (coming as parameter) in my CustomAuthorize class.
 
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