Dim request As HttpWebRequest
        Dim response As HttpWebResponse
        request = CType(WebRequest.Create("https://xxx.yyy.com/api/2.2/auth/signin"), HttpWebRequest)
        request.ContentType = "application/x-www-form-urlencoded"
        request.ContentLength = postData.Length
        request.Method = "POST"
        request.AllowAutoRedirect = False
        Dim requestStream As Stream = request.GetRequestStream()
        Dim postBytes As Byte() = System.Text.Encoding.ASCII.GetBytes(postData)
        requestStream.Write(postBytes, 0, postBytes.Length)
        requestStream.Close()
        response = CType(request.GetResponse(), HttpWebResponse)

        Dim s As String = New StreamReader(response.GetResponseStream()).ReadToEnd()