1. Inside your layout, add a Login button with the following code:
<com.twitter.sdk.android.core.identity.TwitterLoginButton
    android:id="@+id/twitter_login_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"/>
  1. In the Activity or Fragment that displays the button, you need to create and attach a Callback to the Login Buttonas the following:
import com.twitter.sdk.android.core.Callback;
import com.twitter.sdk.android.core.Result;
import com.twitter.sdk.android.core.TwitterException;
import com.twitter.sdk.android.core.TwitterSession;
import com.twitter.sdk.android.core.identity.TwitterLoginButton;
...

loginButton = (TwitterLoginButton) findViewById(R.id.login_button);
loginButton.setCallback(new Callback<TwitterSession>() {
    @Override
    public void success(Result<TwitterSession> result) {
        Log.d(TAG, "userName: " + session.getUserName());
        Log.d(TAG, "userId: " + session.getUserId());
        Log.d(TAG, "authToken: " + session.getAuthToken());
        Log.d(TAG, "id: " + session.getId());
        Log.d(TAG, "authToken: " + session.getAuthToken().token);
        Log.d(TAG, "authSecret: " + session.getAuthToken().secret);
    }

    @Override
    public void failure(TwitterException exception) {
        // Do something on failure
    }
});
  1. Pass the result of the authentication Activity back to the button:
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    // Make sure that the loginButton hears the result from any
    // Activity that it triggered.
    loginButton.onActivityResult(requestCode, resultCode, data);
}

Note, If using the TwitterLoginButton in a Fragment, use the following steps instead:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    // Pass the activity result to the fragment, which will then pass the result to the login
    // button.
    Fragment fragment = getFragmentManager().findFragmentById(R.id.your_fragment_id);
    if (fragment != null) {
        fragment.onActivityResult(requestCode, resultCode, data);
    }
}
  1. Add the following lines to your build.gradle dependencies:
apply plugin: 'io.fabric'

repositories {
    maven { url '<https://maven.fabric.io/public>' }
}

compile('com.twitter.sdk.android:twitter:1.14.1@aar') {
    transitive = true;
}