Hi Friend...
There are multiple technique you can do it..
using session object- Once authentication is done you will get username and password in session and get it on another page..
Example-:
Using Session Variable..
Session Created on first page
Session["UserName"] = txtName.Text;
Response.Redirect("WebForm2.aspx");
Below code shows how to get session value on another page..
this code must be placed on second page(WebForm2.aspx)
if(Session["UserName"] != null)
Label3.Text = Session["UserName"].ToString();
If you don't want store values in label(if want to store values in label and don't want to display set visible property false) use hiddenfield for store values...I think, it's the best way..
Just like above code you can also store and get password on another page..