def temp_url(object_key, temp_url_key, expires_at = Time.now.to_i + 60)
      private_url("GET", object_key, temp_url_key, expires_at)
    end
def temp_url(object_key, temp_url_key, expires_at = Time.now.to_i + 60)
      private_url("GET", object_key, temp_url_key, expires_at)
    end
Generate an expiring URL for downloading a file that is otherwise private.
 Useful for providing temporary access to files.