docs: def pre_flight_headers(self, request, methods):
          # type: (BaseHttpRequest, Sequence[api.Method]) -> Dict[str, str]
          """
          Generate pre-flight headers.
          """
          methods = ', '.join(m.value for m in methods)
          headers = {
              'Allow': methods,
              'Cache-Control': 'no-cache, no-store'
          }
  
          allow_origin = self.allow_origin(request)
          if allow_origin:
              headers = dict_filter(headers, {
                  'Access-Control-Allow-Origin': allow_origin,
                  'Access-Control-Allow-Methods': methods,
                  'Access-Control-Allow-Credentials': {True: 'true', False: 'false'}.get(self.allow_credentials),
                  'Access-Control-Allow-Headers': ', '.join(self.allow_headers) if self.allow_headers else None,
                  'Access-Control-Expose-Headers': ', '.join(self.expose_headers) if self.expose_headers else None,
                  'Access-Control-Max-Age': str(self.max_age) if self.max_age else None,
              })
  
          return headers