code: func (h *handler) signAndSend(ctx context.Context, json string) error {
  	// TODO(mpl): sign things ourselves if we can.
  	scl, err := h.cl.Sign(ctx, h.server, strings.NewReader("json="+json))
  	if err != nil {
  		return fmt.Errorf("could not get signed claim %v: %v", json, err)
  	}
  	if _, err := h.cl.Upload(ctx, client.NewUploadHandleFromString(string(scl))); err != nil {
  		return fmt.Errorf("could not upload signed claim %v: %v", json, err)
  	}
  	return nil
  }
docs: // TODO(mpl): move that to client pkg, with a good API ?