Download A Page Lose Authentication/session State?

I have an issue of keeping the authentication and session state on a downloaded page, on the same website.

I have 2 pages, page 1 will download page 2, using the following code:

Page 1 code:

System.Net.WebClient webClient = new System.Net.WebClient();
byte[] buffer = webClient.DownloadData("http://www.mywebsite.co.uk/page2.aspx");
return Encoding.UTF8.GetString(buffer);

but the authentication is lost, so i needed to re-login in page 2 by writing auto login code myself.

But then the session is lost, so the session variables set in page 1 cannot be share to page 2, and vice versa.