code: public function execute()
      {
          $result = $this->resultJsonFactory->create();
          try {
              $activeVersion = $this->getRequest()->getParam('active_version');
              $dictionaryName = Config::AUTH_DICTIONARY_NAME;
              $dictionary = $this->api->getSingleDictionary($activeVersion, $dictionaryName);
  
              if ((is_array($dictionary) && empty($dictionary)) || $dictionary == false || !isset($dictionary->id)) {
                  return $result->setData([
                      'status'    => 'empty',
                      'msg'       => 'Basic Authentication cannot be enabled because there are no users assigned to it.'
                  ]);
              } else {
                  $authItems = $this->api->dictionaryItemsList($dictionary->id);
  
                  if (is_array($authItems) && empty($authItems)) {
                      return $result->setData([
                          'status' => 'empty',
                          'msg'    => 'Basic Authentication cannot be enabled because there are no users assigned to it.'
                      ]);
                  }
  
                  return $result->setData(['status' => true]);
              }
          } catch (\Exception $e) {
              return $result->setData([
                  'status'    => false,
                  'msg'       => $e->getMessage()
              ]);
          }
      }
docs: Check if authentication users are available
  
  @return \Magento\Framework\Controller\Result\Json