Managing user session in C# ASP.net

protected void btnLogin_Click(object sender, EventArgs e)
    {
        if (txtUsername.Text != "" && txtPassword.Text != "")
        {
            RegistrationUser Dataservice = new RegistrationUser();
            DataTable dtGetlogDetail = Dataservice.GetLoginDetail(txtUsername.Text, txtPassword.Text);
            if (dtGetlogDetail.Rows.Count > 0)
            {
                if (dtGetlogDetail.Rows[0]["confirmed"].ToString() == "1")
                {
                    Session["User"] = Convert.ToInt32(dtGetlogDetail.Rows[0]["id"]);
                    Response.Redirect("~/Customer/ClientIndex.aspx");
                }
            }
            else
            {
                Response.Write("<script>alert('Please enter valid Password or Username.')</script>");
            }
        }
    }

protected void btnLogOut_Click(object sender, EventArgs e)
{
 if (Session["User"] != null)
        {
            Session.Clear();//clear session
            Session.Abandon();//Abandon session
            Response.Cache.SetExpires(DateTime.UtcNow.AddMinutes(-1));
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.Cache.SetNoStore();          
        }
}