public function callback(Request $request, Lastfm $lastfm)
{
abort_unless($token = $request->input('token'), 500, 'Something wrong happened.');
// Get the session key using the obtained token.
abort_unless($sessionKey = $lastfm->getSessionKey($token), 500, 'Invalid token key.');
$this->auth->user()->savePreference('lastfm_session_key', $sessionKey);
return view('api.lastfm.callback');
}