private void btn_save_Click(object sender, EventArgs e)
{
string userName = tb_userName.Text;
string password = Crypting.EncryptSecret(tb_password.Text);
Configuration configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
configuration.AppSettings.Settings["UserName"].Value = userName;
configuration.AppSettings.Settings["Password"].Value = password;
configuration.Save(ConfigurationSaveMode.Full, true);
ConfigurationManager.RefreshSection("appSettings");
this.Close();
}