//Implements OnRequestPermissionsResultCallback for automatic handling android M runtime permissions
public class MyActivity extends Activity implements ActivityCompat.OnRequestPermissionsResultCallback{

    private WebAuthProvider provider;
    private Auth0 account;
    private AuthCallback callback;

    @Override
    protected void onCreate(Bundle savedInstanceState)  {
        super.onCreate(savedInstanceState);
        provider = WebAuthProvider.from(account, callback)
                .useBrowser(true)
                .useCodeGrant(true) //pkce usage is forced on 'code' grant type
                .withState("123456");
        //Need to keep the instance for permission request results parsing

        provider.start(this, "twitter", 123);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        provider.onRequestPermissionsResult(this, requestCode, permissions, grantResults);
    }
}