C# Login request

I'm trying to login to this website https://idp.bexio.com/login using http webrequest. This is my current code. I've done alot of research but none of it seems to fit these needs.

   CookieContainer cc = new CookieContainer();
        Uri uri = new Uri("https://office.bexio.com/oauth/authorize?client_id=Client_ID&redirect_uri=https://office.bexio.com&state=STATE&scope=SCOPE&response_type=code");
        string data = "login-form.j_username=xxxxx&login-form.j_password=xxxxx";
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(uri);
        request.CookieContainer = cc;
        request.Method = WebRequestMethods.Http.Post;
        request.ContentLength = data.Length;
        request.ContentType = "application/x-www-form-urlencoded";
        StreamWriter writer = new StreamWriter(request.GetRequestStream());
        writer.Write(data);
        writer.Close();
        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        StreamReader reader = new StreamReader(response.GetResponseStream());
        string tmp = reader.ReadToEnd();
        response.Close();
        Console.WriteLine(tmp);

The resposne I'm getting is just the login page, and not the logged in page as I want. Any help is appreciated.

Thanks in advance