Integrating Facebook chat

Question

I have written a program to integrate Facebook user chat in C#, however I always get <failure xmlns="urn:ietf:params:xml:ns:xmpp-sasl"><not-authorized/></failure> after sending the response to the server.

I've checked the API key and the App secret, both of them are correct. It looks like I'm passing some wrong parameters to the server.

Here is my code.

private void GetDetailsButton_Click(object sender, EventArgs e)
{
     TcpClient FacebookClient = new TcpClient();
     FacebookClient.Connect("chat.facebook.com", 5222);
     NetworkStream myns = FacebookClient.GetStream();

     string xml = "<?xml version='1.0'?>" +
     "<stream:stream " +
     "id='1' " +
     "to='chat.facebook.com' " +
     "xmlns='jabber:client' " +
     "xmlns:stream='http://etherx.jabber.org/streams' " +
     "version='1.0' >";

     StreamWriter mySw = new StreamWriter(myns);
     mySw.WriteLine(xml);  //sending initial request
     mySw.Flush();

     byte[] serverResponseByte = new byte[1024];
     int myBytesRead = 0;
     StringBuilder myResponseAsSB = new StringBuilder();

     //reading response from the server to see the supported authentication methods 
     do
     {
            myBytesRead = myns.Read(serverResponseByte, 0, serverResponseByte.Length);
            myResponseAsSB.Append(System.Text.Encoding.UTF8.GetString(serverResponseByte, 0, myBytesRead));

     } while (myns.DataAvailable);


     myResponseAsSB.Clear();

     xml = "<auth " +
     "xmlns='urn:ietf:params:xml:ns:xmpp-sasl' " +
     "mechanism='X-FACEBOOK-PLATFORM'  />";

     mySw.WriteLine(xml);
     mySw.Flush();   //sending response to server to use X-FACEBOOK-PLATFORM


     //reading challenge send by the server
     do
     {
          myBytesRead = myns.Read(serverResponseByte, 0, serverResponseByte.Length);
          myResponseAsSB.Append(System.Text.Encoding.UTF8.GetString(serverResponseByte, 0, myBytesRead));

     } while (myns.DataAvailable);


     myResponseAsSB.Replace("<challenge xmlns=\"urn:ietf:params:xml:ns:xmpp-sasl\">", "");
     myResponseAsSB.Replace("</challenge>", "");

     //converting challenge string to normal string
     byte[] myregularstrigbytes = Convert.FromBase64String(myResponseAsSB.ToString());
     string myregularstring = System.Text.Encoding.UTF8.GetString(myregularstrigbytes);


     //I've hardcoded the accesstoken here for testing purpose. 
     string SessionKey = AccessToken.Split('|')[1]; 

     string response = ComposeResponse(myregularstring);

     byte[] myResponseByte = Encoding.UTF8.GetBytes(response.ToString());

     string myEncodedResponseToSend = Convert.ToBase64String(myResponseByte);
     xml = String.Format("<response xmlns=\"urn:ietf:params:xml:ns:xmpp-sasl\">{0}</response>", myEncodedResponseToSend);
     mySw.WriteLine(xml);
     mySw.Flush();   //sending the response to the server with my parameters

     myResponseAsSB.Clear();

     //checking if authentication succeed 
     do
     {
          myBytesRead = myns.Read(serverResponseByte, 0, serverResponseByte.Length);
          myResponseAsSB.Append(System.Text.Encoding.UTF8.GetString(serverResponseByte, 0, myBytesRead));

     } while (myns.DataAvailable);

     MessageBox.Show(myResponseAsSB.ToString());

}

    private string ComposeResponse(string serverresponse)
    {
         string version = serverresponse.Split('&')[0].Split('=')[1];
         string method = serverresponse.Split('&')[1].Split('=')[1];
         string nonce = serverresponse.Split('&')[2].Split('=')[1];
         string SessionKey = AccessToken.Split('|')[1];

         long callId = (long)(DateTime.UtcNow - new DateTime(1970, 1, 1)).TotalSeconds;

         string sig = "api_key=" + appId
         + "call_id=" + callId
         + "method=" + method
         + "nonce=" + nonce
         + "session_key=" + SessionKey
         + "v=" + "1.0"
         + AppSecret;

         MD5 md = MD5.Create();
         var hash = md.ComputeHash(Encoding.UTF8.GetBytes(sig));

         sig = hash.Aggregate("", (current, b) => current + b.ToString("x2"));

         return "api_key=" + HttpUtility.UrlEncode(appId)
         + "&call_id=" + HttpUtility.UrlEncode(callId)
         + "&method=" + HttpUtility.UrlEncode(method)
         + "&nonce=" + HttpUtility.UrlEncode(nonce)
         + "&session_key=" + HttpUtility.UrlEncode(SessionKey)
         + "&v=" + HttpUtility.UrlEncode("1.0")
         + "&sig=" + HttpUtility.UrlEncode(sig);

    }

I've refereed to this articles Facebook Chat Authentication in C# and X-FACEBOOK-PLATFORM and my application type is of Native/Desktop.

Can some point me in the right direction?

Edit : I think the problem is while creating the signature, is there any way to verify the created signature?

Edit 1 : According to this SO answer the access token contains the session key after the first | character and I could find the | character till 2 days ago, but now I can't find the | character in the access token, its really strange, so how do I find the session key now? (Or may be I should go to sleep now.)

Edit 2 : Its strange that I always got the access token in form of <appId>|<sessionKey>|<digest> for native/desktop application. I did further searching and found out that the session key needs to be extracted from auth.promoteSession legacy api and encode the parameters using HttpUtility.UrlEncode instead of HttpUtility.HtmlEncode.

Now I've hard coded the Access token (verified it in the Access Token Debugger), the session key, App key and app secret still I get the same error <failure xmlns="urn:ietf:params:xml:ns:xmpp-sasl"><not-authorized/></failure>

Edit 3 : I have been banging my head over a week and still this doesn't work, but today I found a update in the documentation which says Note that this needs to be over TLS (Transport Layer Security) or you'll get an error. I guess I need to modify my code accordingly.

Edit 4 : I've tried out the code in the documentation and found that the value of $SESSION_XML should be

$SESSION_XML = '<iq type="set" id="4">'.
  '<session xmlns="urn:ietf:params:xml:ns:xmpp-session"/></iq>';

I will post the C# code once I finish converting it.

Answer 1

To use X-FACEBOOK-PLATFORM you will need the user session which is provided with the legacy auth flow. However, the access_token contain the user session after the | as you noted in your edit1.

We announced in the last blog post that access_token will be encrypted and this will be mandatory from Octber 1st. Until then, the option can be toggle in the Advanced App settings http://developers.facebook.com/blog/post/553/.

Moving forward, access_token will be able to be use for X-FACEBOOK-PLATFORM.

Answer 2

You'll get farther faster if you start with an existing XMPP library. Here is a list: http://xmpp.org/xmpp-software/libraries/

For example, you're going to wish you hadn't hand-coded all of your XML instead of running it through the DOM very soon. In the meantime, test all of your inputs with these characters: <>'"&