how to update role of location path in web config using parameter textbox in c# ?

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C#

ASP.NET

how if when everytime i click update .. i can role update automatically .. like below :

<location path="page1">
    <system.web>
      <authorization>
        <allow users="role1, role2, role 3, ..." />
        <deny users="*" />
      </authorization>
    </system.web>
  </location>

so far below my code for updating , but it's yet for updating role

private void UpdateLocation(AuthorizationRule newRule, string location, string role)
   {
       string path = Server.MapPath("~/Web.Config");
       XmlDocument xDoc = new XmlDocument();
       xDoc.Load(path);
       XmlNodeList list = xDoc.DocumentElement.SelectNodes("location");
       if (list.Count > 0)
       {
           XmlNode node = list[0];
           XmlAttribute attribute = node.Attributes["path"];
           attribute.Value = this.txtLocation.Text.Trim();
           node.Attributes.Append(attribute);
           xDoc.Save(path);
       }
       else
       {//create location element and the path attribute with it's value set to the
           //selected page
           XmlElement newLocationelement = xDoc.CreateElement("location");
           XmlAttribute newLocationAttrib = xDoc.CreateAttribute("path");
           newLocationAttrib.Value = location;
           newLocationelement.Attributes.Append(newLocationAttrib);
           XmlElement newSystemWebelement = xDoc.CreateElement("system.web");
           XmlElement newAuthorizationelement = xDoc.CreateElement("authorization");
           //create the allow element
           XmlElement newAllowelement = xDoc.CreateElement("allow");
           XmlAttribute newAllowAttrib = xDoc.CreateAttribute("users");
           newRule.Roles.Add(role).ToString();
           string listofRoles = "";
           foreach (var item in newRule.Roles)
           {
               listofRoles = item.ToString();
           }
           newAllowAttrib.Value = listofRoles;
           newAllowelement.Attributes.Append(newAllowAttrib);
           //create the deny element
           XmlElement newDenyelement = xDoc.CreateElement("deny");
           XmlAttribute newUsersAttrib = xDoc.CreateAttribute("users");
           newUsersAttrib.Value = "*";
           newDenyelement.Attributes.Append(newUsersAttrib);
           newAuthorizationelement.AppendChild(newAllowelement);
           newAuthorizationelement.AppendChild(newDenyelement);
           newLocationelement.AppendChild(newSystemWebelement);
           newSystemWebelement.AppendChild(newAuthorizationelement);
           xDoc.DocumentElement.AppendChild(newLocationelement);
           xDoc.PreserveWhitespace = true;
           //write to web.config file using xml writer
           XmlTextWriter xwriter = new XmlTextWriter(path, null);
           xDoc.WriteTo(xwriter);
           xwriter.Close();

       }
   }