X-FACEBOOK-PLATFORM authentication with SMACK Java library using OAuth 2.0

First post here so please be gentle. I'm building a facebook chat client, using Smack library. I'm using X-FACEBOOK-PLATFORM method in order not to save any passwords. I had it working properly using oauth 1.0, and want to change it to 2.0, cause of the october 1st deadline ;p. From what I understand the only thing I'd have to do in order to migrate to 2.0 is removing "sig" and "session_key" parameters and adding an "access_token" parameter, but I'm getting an "SASL authentication X-FACEBOOK-PLATFORM failed: not-authorized:". I'm using this custom SASLMechanism class:

package smackresearching;
import java.io.IOException;
import java.net.URLEncoder;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.Map;

import javax.security.sasl.Sasl;

import org.jivesoftware.smack.SASLAuthentication;
import org.jivesoftware.smack.XMPPException;
import org.jivesoftware.smack.sasl.SASLMechanism;
import org.jivesoftware.smack.util.Base64;

public class SASLXFacebookPlatformMechanism extends SASLMechanism {

    public static final String NAME = "X-FACEBOOK-PLATFORM";
    private String apiKey = "";
        private String accessToken = "";


    /**
     * Constructor.
     */
    public SASLXFacebookPlatformMechanism(SASLAuthentication saslAuthentication) {
            super(saslAuthentication);
    }

    @Override
    protected void authenticate() throws IOException, XMPPException {
        // Send the authentication to the server
        getSASLAuthentication().send(new AuthMechanism(getName(), ""));
    }

    @Override
    public void authenticate(String apiKey, String host, String accessToken) throws IOException, XMPPException {
        this.apiKey = apiKey;
        this.accessToken = accessToken;
        this.hostname = host;

        String[] mechanisms = { "DIGEST-MD5" };
        Map<String, String> props = new HashMap<String, String>();
        this.sc = Sasl.createSaslClient(mechanisms, null, "xmpp", host, props,