A simple proxy

There is a task - to write a simple proxy server. Well, this task is 'almost' completed. I think i'm re-inventing the wheel but I don't mind, my proxy works like this:

There's a HttpListener that listens and launches a processing thread at web request of a client. Then the processing thread forms a WebRequest to the necessary site, downloads its contents, removes all the flash, tops, counters and adclicks and returns it all to the client.

As I said this 'almost' works. The problems start when I need to get an authorization on some resource (web mail or forum or whatever).

So, the first question is whether am I doing everything right with cookies:

vb Code:

Dim CookieCont As CookieContainer = Nothing
        If DownStream_Request.Cookies.Count <> 0 Then
            CookieCont = New CookieContainer
 
            Dim c As Cookie
            For Each c In DownStream_Request.Cookies
                If c.Domain = "" Then
                    c.Domain = UB.Host
                End If
                CookieCont.Add(c)
            Next
        End If
 
        UpStream_Request.CookieContainer = CookieCont

The second question - I'm not sure if I process POST requests right:

vb Code:

If DownStream_Request.HttpMethod.ToLower = "post" Then
 
                UpStream_Request_Stream = UpStream_Request.GetRequestStream
                DownStream_Request_Stream = DownStream_Request.InputStream
 
                Do
                    bytesRead = DownStream_Request_Stream.Read(buffer, 0, buffer.Length)
                    UpStream_Request_Stream.Write(buffer, 0, bytesRead)
                    If bytesRead = 0 Then
                        UpStream_Request_Stream.Flush()
                        UpStream_Request_Stream.Close()
                        DownStream_Response.Redirect(requested_uri.ToString)
                        DownStream_Response.Close()
                        ThreadCol.Remove(mythread)
                        Exit Sub
                    End If
                Loop
            End If

Anyway, I don't understand what else should I do in order to get authorizations on forums and mail work properly.