def sign
      raise "this URL is already signed !" if signed?

      # build new url
      signed_url = url.dup
      signed_url.query = extended_query
      signed_url
    end
def sign
      raise "this URL is already signed !" if signed?

      # build new url
      signed_url = url.dup
      signed_url.query = extended_query
      signed_url
    end
:nodoc: