retrieve username from Session

I am using siteminder and trying to retrieve the userid
protected void Page_Load(object sender, EventArgs e)     {         var headers = String.Empty;         foreach (var key in Request.Headers.AllKeys)             headers += key + "=" + Request.Headers[key] + Environment.NewLine;         //TextBox1.Text = headers["USER_UID"];         TextBox1.Text = headers;         //TextBox2.Text = Request.Headers[KeyedByTypeCollection];     }

Now in textbox1 I am getting all the header info generated. How can I retrieve just the username/id/email..Tried above. Any suggestions much helpful.
Thanks Much,
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