Session authentication code - Asp.net

[Justin]

1st page - default.aspx
===================

protected void Button1_Click(object sender, EventArgs e)
{

if (TextBox1.Text == "aa")
{
s = TextBox1.Text;
Session["authenticate"] = true;

Session["username"] = TextBox1.Text;
Response.Redirect("UserHome.aspx");
}

else
Label1.Text = "Oops wrong password/username";
}

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1st page - UserHomeaspx
====================

if(Session.Keys.Count==0)
Response.Write("Sorry u have not logged in");

else
Response.Write("logged in");
===================