Here is the situation.
I'm using Forms authentication mode.
I have a webform with a WebDataGrid which has Sorting bahavior enabled.
I let the authentication timeout expire, then click on a column header to sort.
The problem is that the AJAX wait indicator is displayed forever and nothing happens.
Also, the grid client event AJAXResponse is never fired.
How can I trap an authentication timeout and redirect the user to the login page ?

I *think* I did manage to detect the timeout in Global.asax using this code

protected void Application_AuthenticateRequest(Object sender, EventArgs e)
{
  if (!Request.IsAuthenticated &&
      null != Request.Headers["Cookie"] &&
      Request.Headers["Cookie"].IndexOf(FormsAuthentication.FormsCookieName) >= 0 &&
      Request.Path != FormsAuthentication.LoginUrl)
  {
    // detect if it's an infragistics ajax callback
    if (Request.Form.AllKeys.Any(x => x.StartsWith("__IGCallback")))
    {
      // now what ??
    }
    // redirect to login
    else
      LoginManager.RedirectToLogin(LoginManager.ReasonType.Expired);
  }
}

But then what do I need to do to inform the client grid that a timeout occured ?