public async Task DoWorkAsync(CancellationToken stoppingToken)
 {
     while (!stoppingToken.IsCancellationRequested)
     {
         //var image = _restClient.GetFile(fileName);
         var files = _restClient.GetDefaultFiles();
         if (files != null)
         {
             foreach (string fileName in files)
             {
                 var image = _restClient.GetFile(fileName);
                 if (image != null)
                 {
                     //var cashKey = $"image_{DateTime.UtcNow:yyy_MM_dd}";
                     var cashKey      = _creator.GetKey(fileName);
                     var entryOptions = new MemoryCacheEntryOptions()
                     {
                         AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(_option.Value.ExpirationTimeValueInMinutes)
                     };
                     _cash.Set(cashKey, image, entryOptions);
                 }
             }
         }
         await Task.Delay(TimeSpan.FromMinutes(_option.Value.ScanningPeriodInMinutes));
     }
 }