if ("POST".Equals(Request.HttpMethod))
{
    Session["ExpriedToken"] = Guid.NewGuid().ToString();
    Response.Redirect("~/Test.aspx");
}

<script type="text/javascript">
        $.get('GetToken.ashx?t=' + new Date().getTime(), function (result) {
            if (result && result != '') {
                alert('重复加载');
                window.location.replace('Expried.aspx');
            }
        });
    </script>

public void ProcessRequest(HttpContext context)
{
    string token = context.Session["ExpriedToken"] as String;
    if (!String.IsNullOrEmpty(token)) context.Session["ExpriedToken"] = null;
    context.Response.Write(token);
}