Cross Domain/Platform Authentication and Data Transfer

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class LandingPage1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
            return;

        //make sure user is not authenticated when the third party program starts.
        FormsAuthentication.SignOut();

        //request for the AuthenticationID
        string AuthenticationID = Request.QueryString["AuthID"];
        if (AuthenticationID == null)
        {
            lblError.Text = "A required parameter is missing from url. ";
            return;
        }
        //Request p1 and p2 from Url. p1 and p2 are the parameters that the third party app needs
        string p1 = Request.QueryString["Para1"].ToString();
        string p2 = Request.QueryString["Para1"].ToString();
        //additional code here to process the parameters

        //Add a web reference to your app and name it anything you like. Here it is named as AuthenticationService. 
        //declare web service and a reference variable - ReturnMessage
        AuthenticationService.AuthenticationService AuthService = new AuthenticationService.AuthenticationService();
        string ReturnMessage = "";
        DataSet ds = null;
        //Call Web Method: RetrieveUserDataSet
        //success: user authenticated, get a DataSet. 
        //Failure: user not authenticated or Url exipred. Return null and error message.
        try
        {
            ds = AuthService.RetrieveUserDataSet(ref ReturnMessage, AuthenticationID);
        }
        catch (Exception ex)
        {
            lblError.Text += ex.Message.ToString();
        }

        if (ReturnMessage != "")
        {
            lblError.Text += ReturnMessage;
            return;
        }
        if (ds != null)
        {
            //depending on the stored procedure used to retrieve the data
            //The DataSet can contain multiple tables 
            //Write code here to loop through the DataSet
            //insert or update the third party database
            //and then programmatically log in the user 
            //by setting up appropriate cookies and session variables
            //For asp.net form authentication, call SetAuthCookie method
            FormsAuthentication.SetAuthCookie("LoginUser", false);

            //display user data for demo purpose
            gvUserData.DataSource = ds.Tables[0];
            gvUserData.DataBind();
        }
        else
        {
            lblError.Text += ReturnMessage;
        }
   
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        //display authentication status
        //display authentication status
        if (!Request.IsAuthenticated)
            lblError.Text = "The user is not authenticated";
        else
            lblError.Text = "The user is authenticated";
    }
}