Here is a modification for the prev. answer. The main difference is when the user is not authenticated, it uses the original "HandleUnauthorizedRequest" method to redirect to login page:
protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
{
if (filterContext.HttpContext.User.Identity.IsAuthenticated) {
filterContext.Result = new RedirectToRouteResult(
new RouteValueDictionary(
new
{
controller = "Account",
action = "Unauthorised"
})
);
}
else
{
base.HandleUnauthorizedRequest(filterContext);
}
}