Cross Domain/Platform Authentication and Data Transfer

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Specialized;


public partial class login : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            lblReturnUrl.Text =( Request.QueryString["ReturnUrl"]??"").ToString();
            lblSiteID.Text = (Request.QueryString["SiteID"] ?? "").ToString();
            if (lblReturnUrl.Text == ""||lblSiteID.Text=="")
            {
                lblError.Text = "The ReturnUrl or SiteID is missing. Can't proceed.";
                btnLogin.Enabled = false;
                return;
            }
            txtUserName.Focus();
            //provide testing accounts for user to log in
            lblError.Text = "Login credentials:<br>user: johnd    pw: password or user: janed   pw: password";
        }
    }
    protected void btnLogin_Click(object sender, EventArgs e)
    {
        try
        {
            DataTable tbl = Authentication.VerifyCredentials(txtUserName.Text, txtPassword.Text);
            
            if (tbl.Rows.Count>0)
            {
                int MinutesToExpire = 1;//Authentication will expire in 1 minute. Can be set to other values
                ProcessAuthenticationData(tbl, MinutesToExpire, Convert.ToInt16(lblSiteID.Text), lblReturnUrl.Text);

            }
            else
            {
                lblError.Text = "No user with these credentials has been found.";
            }
        }
        catch (Exception ex)
        {
            lblError.Text = ex.Message.ToString();
        }

    }
    private void ProcessAuthenticationData(DataTable tbl, int minutesToExpire, int siteID, string returnUrl)
    {
        //place user data into a collection which is easy to handle
        NameValueCollection UserData = Authentication.BuildUserDataCollection(tbl, minutesToExpire, siteID, returnUrl);

        //build all data into a text string so that it can be stored in database
        string UserString = Authentication.SerializeParameters(UserData);

        //Save querystring parameter and user data string
        string AuthenticationID = Guid.NewGuid().ToString().Replace("-", "");
        //save user information. When the third party app calls web service, this information will be retrieved
        Authentication.ExecuteNonQuery("AuthenticationLog_Insert", new object[] { AuthenticationID, UserString});
        
        Response.Redirect(Authentication.WellFormReturnUrl(lblReturnUrl.Text, AuthenticationID));
    }
}