code: func (d Datastore) Download(ctx context.Context, path string, param *soap.Download) (io.ReadCloser, int64, error) {
  	u, p, err := d.downloadTicket(ctx, path, param)
  	if err != nil {
  		return nil, 0, err
  	}
  	return d.Client().Download(ctx, u, p)
  }
docs: // Download via soap.Download with an http service ticket