code: public function getApplicationApiService()
      {
          $applicationService = new \Greenhouse\GreenhouseToolsPhp\Services\ApplicationService($this->_apiKey, $this->_boardToken);
          $apiClient  = new GuzzleClient(array(
              'base_uri' => ApiService::APPLICATION_URL
          ));
          $applicationService->setClient($apiClient);
          
          return $applicationService;
      }
docs: The Appliction API Service handles posting applications in to Greenhouse.  This
  requires your API key to be set.