code: public function getByKey($key = null)
      {
          if (!array_key_exists($key, $this->applicationMap)) {
              $this->applicationMap[$key] = array();
              $config = $this->serviceManager->get('Config');
              $appConfig = $this->serviceManager->get('ApplicationConfig');
              foreach ($appConfig['modules'] as $module) {
                  if (array_key_exists($module, $config)) {
                      if (array_key_exists($key, $config[$module])) {
                          // The strtolower is essential for later retrieving
                          // namespaces in the repositories
                          // anyway, it's easier to agree everything should be lowercase
                          $this->applicationMap[$key][strtolower($module)] = $config[$module][$key];
                      }
                  }
              }
          }
          return $this->applicationMap[$key];
      }
docs: fetch the settings for a certain key of all Modules
  @param string $key
  @return array