public function onlineId() : string
    {
        if ($this->onlineId === null) {
            $response = $this->httpClient()->get(sprintf(User::USERS_ENDPOINT . 'profile2', 'me'), [
                'fields' => 'onlineId'
            ]);

            $this->onlineId = $response->profile->onlineId;
        }
        return $this->onlineId;
    }