I'm trying to integrate Yahoo into my application. I want them to login using their Yahoo accounts because I will be needing their names later in the application. But whenever I request for a token, I receive the following errors:

getRequestToken() Exception: oauth.signpost.exception.OAuthCommunicationException: 
Communication with the service provider failed: Service provider responded in error: 400 (Bad Request)

Here is my code (Request_Token_Activity.java):

import oauth.signpost.OAuth;
import oauth.signpost.OAuthConsumer;
import oauth.signpost.OAuthProvider;
import oauth.signpost.commonshttp.CommonsHttpOAuthConsumer;
import oauth.signpost.commonshttp.CommonsHttpOAuthProvider;
import oauth.signpost.signature.HmacSha1MessageSigner;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.net.Uri;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;

public class Request_Token_Activity extends Activity {
    private OAuthConsumer consumer; 
    private OAuthProvider provider;
    private SharedPreferences prefs;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    try {

        consumer = new CommonsHttpOAuthConsumer("my consumer key", "my consumer secret");
        consumer.setMessageSigner(new HmacSha1MessageSigner()); 
        provider = new CommonsHttpOAuthProvider(
                "http://api.login.yahoo.com/oauth/v2/get_request_token",
                "http://api.login.yahoo.com/oauth/v2/get_token",
                "http://api.login.yahoo.com/oauth/v2/request_auth");

    } catch (Exception e) {
        Log.e("", "onCreate Exception: " + e.toString());
    }
    getRequestToken();
}
private void getRequestToken() {
    try {

        String url = provider.retrieveRequestToken(consumer, "yahooapi://callback");
        Log.i("", "Yahoo URL: " + url);
        Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url)).setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP | Intent.FLAG_ACTIVITY_NO_HISTORY | Intent.FLAG_FROM_BACKGROUND);
        this.startActivity(intent);
    } catch (Exception e) {
        Log.i("", "getRequestToken() Exception: " + e.toString());
    }
}
@Override
public void onNewIntent(Intent intent) {
    super.onNewIntent(intent); 
    prefs = PreferenceManager.getDefaultSharedPreferences(this);
    final Uri uri = intent.getData();
    if (uri != null && uri.getScheme().equals("yahooapi")) {
        getAccessToken(uri);
    }
}
private void getAccessToken(Uri uri) {
    final String oauth_verifier = uri.getQueryParameter(OAuth.OAUTH_VERIFIER);
    try {
        provider.retrieveAccessToken(consumer, oauth_verifier);

        final Editor edit = prefs.edit();
        edit.putString("YAHOO_OAUTH_TOKEN", consumer.getToken());
        edit.putString("YAHOO_OAUTH_TOKEN_SECRET", consumer.getTokenSecret());
        edit.commit();

        String token = prefs.getString("YAHOO_OAUTH_TOKEN", "");
        String secret = prefs.getString("YAHOO_OAUTH_TOKEN_SECRET", "");
        consumer.setTokenWithSecret(token, secret);

        Log.i("", "Yahoo OAuth Token: " + token);
        Log.i("", "Yahoo OAuth Token Secret: " + token);

    } catch (Exception e) {
        Log.i("", "getAccessToken Exception: " + e.toString());
    }
}

}

And this is a snapshot of my AndroidManifest.xml:

        <activity android:name="Request_Token_Activity" android:launchMode="singleTask">
        <intent-filter>
            <action android:name="android.intent.action.VIEW" />
            <category android:name="android.intent.category.DEFAULT" />
            <category android:name="android.intent.category.BROWSABLE" />
            <data android:scheme="yahooapi" android:host="callback" />
        </intent-filter>
    </activity>

I have set-up my Yahoo Project as a Web Application and put Read and Write access to Social and Contacts. What am I doing wrong?