code: def _get_request_param(self, request):
          
          params = {}
          try:
              params = request.POST.copy()
              if not params:
                  params = json.loads(request.body)
          except Exception:
              pass
          for key in params:
              # replace a value to a masked characters
              if key in self.mask_fields:
                  params[key] = '*' * 8
  
          # when a file uploaded (E.g create image)
          files = request.FILES.values()
          if list(files):
              filenames = ', '.join(
                  [up_file.name for up_file in files])
              params['file_name'] = filenames
  
          try:
              return json.dumps(params, ensure_ascii=False)
          except Exception:
              return 'Unserializable Object'
docs: Change POST data to JSON string and mask data.