code: func (s *Signer) SignWithExpiry(uri, expiry string) string {
  	audience := strings.ToLower(url.QueryEscape(uri))
  	sts := stringToSign(audience, expiry)
  	sig := s.signString(sts)
  	return fmt.Sprintf("SharedAccessSignature sr=%s&sig=%s&se=%s&skn=%s", audience, sig, expiry, s.KeyName)
  }
docs: // SignWithExpiry signs a given uri with a given expiry string