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using System.Web.SessionState;
using System.Reflection;

protected void ReGenerateSessionId()
    {
        SessionIDManager manager = new SessionIDManager();
        string oldId = manager.GetSessionID(Context);
        string newId = manager.CreateSessionID(Context);
        bool isAdd = false, isRedir = false;
        manager.RemoveSessionID(Context);
        manager.SaveSessionID(Context, newId, out isRedir, out isAdd);

        HttpApplication ctx = (HttpApplication)HttpContext.Current.ApplicationInstance;
        HttpModuleCollection mods = ctx.Modules;
        System.Web.SessionState.SessionStateModule ssm = (SessionStateModule)mods.Get("Session");
        System.Reflection.FieldInfo[] fields = ssm.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance);
        SessionStateStoreProviderBase store = null;
        System.Reflection.FieldInfo rqIdField = null, rqLockIdField = null, rqStateNotFoundField = null;

        SessionStateStoreData rqItem = null;
        foreach (System.Reflection.FieldInfo field in fields)
        {
            if (field.Name.Equals("_store")) store = (SessionStateStoreProviderBase)field.GetValue(ssm);
            if (field.Name.Equals("_rqId")) rqIdField = field;
            if (field.Name.Equals("_rqLockId")) rqLockIdField = field;
            if (field.Name.Equals("_rqSessionStateNotFound")) rqStateNotFoundField = field;

            if ((field.Name.Equals("_rqItem")))
            {
                rqItem = (SessionStateStoreData)field.GetValue(ssm);
            }
        }
        object lockId = rqLockIdField.GetValue(ssm);

        if ((lockId != null) && (oldId != null))
        {
            store.RemoveItem(Context, oldId, lockId, rqItem);
        }

        rqStateNotFoundField.SetValue(ssm, true);
        rqIdField.SetValue(ssm, newId);
    }

protected void Login_Click(object sender, EventArgs e)
{
    if (/*Login success*/)
    {
        ReGenerateSessionId(); // Change SessionID
        Session["User"] = user;
        Response.Redirect("Login_Success.aspx", true);
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (Session["LoggedIn"] != null)
    {
        lblMessage.Text = "Congratulations !, you are logged in.";
        lblMessage.ForeColor = System.Drawing.Color.Green;
        btnLogout.Visible = true;
    }
    else
    {
        lblMessage.Text = "You are not logged in.";
        lblMessage.ForeColor = System.Drawing.Color.Red;
    }
}

protected void LoginMe(object sender, EventArgs e)
{
    // Check for Username and password (hard coded for this demo)
    if (txtU.Text.Trim().Equals("u") && txtP.Text.Trim().Equals("p"))
    {
        Session["LoggedIn"] = txtU.Text.Trim();
    }
    else
    {
        lblMessage.Text = "Wrong username or password";
    }
}

protected void LogoutMe(object sender, EventArgs e)
{
    Session.Clear();
    Session.Abandon();
    Session.RemoveAll();
}