How to catch the post data sent to the redirect URL (VB 2010) - vb.net

Question

I am trying to login to one web page via my Windows Form application (VB 2010) and get some response, but I don't know how to do it.
The server service is described here:
https://api.developer.betfair.com/services/webapps/docs/display/1smk3cen4v3lu3yomq5qye0ni/Interactive+Login+from+a+Desktop+Application
On beginning I tried to insert WebBrowser Control to my form, but I read many articles, also here, that using BeforeNavigate2 event is an old way.
I would like to do this:
Send HTTP request to webserver including username and password
Catch the post data sent to the redirect URL
Read the POST request body an get loginStatus and productToken (SSOID)
This is my code:
Private Sub getPOST()
' Create a request for the URL
Dim request As WebRequest = _
WebRequest.Create("https://identitysso.betfair.com/view/login?product=82&url=https://www.betfair.com&username=abc&password=abc")
request.Method = "POST"
' Get the response
Dim response As HttpWebResponse = CType(request.GetResponse(), HttpWebResponse)
' Get the stream containing content returned by the server.
Dim dataStream As Stream = response.GetResponseStream()
' Open the stream using a StreamReader for easy access.
Dim reader As New StreamReader(dataStream)
' Read the content.
Dim responseFromServer As String = reader.ReadToEnd()
' Display the content.
RichTextBox1.Text = responseFromServer
' Cleanup the streams and the response.
reader.Close()
dataStream.Close()
response.Close()
End Sub
But this code returns HTML code of page where are not loginStatus and SSOID.

Answer 1

I examined this page and discovered there are a few problems with your code:
First you are posting to the wrong URL because the www.betfair.com/view/login form has action="/api/login", not "/view/login". Second, you are passing your username/password in the QueryString rather than in POSTDATA... this form uses method=post. Third, you are not passing all required fields. This code snippet should remedy these described problems, as well as answer your question about obtaining the redirect URL:
Sub TestWebClient()
' Create a request for the URL
' You were using the wrong URL & passing the values improperly
' I also changed this to HttpWebRequest, used to be WebRequest.
Dim request As HttpWebRequest = WebRequest.Create("https://identitysso.betfair.com/api/login") '
request.Method = "POST"
' New code added
request.ContentType = "application/x-www-form-urlencoded"
' New code added, this prevents the following of the 302 redirect in the Location header
request.AllowAutoRedirect = False
' New code added, this sends the values as POSTDATA, which is contained inside the HTTP POST request rather than in the URL
Using writer As New StreamWriter(request.GetRequestStream)
writer.Write("username=abc")
writer.Write("&password=abc")
writer.Write("&login=true")
writer.Write("&redirectMethod=POST")
writer.Write("&product=82")
writer.Write("&url=https://www.betfair.com/")
writer.Write("&ioBlackBox=")
End Using
' Get the response
' This will print the Location header (aka "Redirect URL") on the screen for you
' Make decisions as needed.
Dim response As HttpWebResponse = request.GetResponse()
Console.WriteLine("HTTP RESPONSE HEADERS:")
For Each item In response.Headers
Console.WriteLine(item & "=" & response.Headers(item))
Next
Console.ReadLine()
End Sub