Say I have the following web.config:
use an xpath query //configuration/system.web/authentication[mode] ?
protected void Page_Load(object sender, EventArgs e)
{
XmlDocument config = new XmlDocument();
config.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
XmlNode node = config.SelectSingleNode("//configuration/system.web/authentication");
this.Label1.Text = node.Attributes["mode"].Value;
}