code: func (wfe *WebFrontEndImpl) addIssuingCertificateURLs(response http.ResponseWriter, issuingCertificateURL []string) error {
  	for _, rawURL := range issuingCertificateURL {
  		parsedURI, err := url.ParseRequestURI(rawURL)
  		if err != nil {
  			return err
  		}
  		parsedURI.Scheme = "https"
  		response.Header().Add("Link", link(parsedURI.String(), "up"))
  	}
  	return nil
  }
docs: // addIssuingCertificateURLs() adds Issuing Certificate URLs (AIA) from a
  // X.509 certificate to the HTTP response. If the IssuingCertificateURL
  // in a certificate is not https://, it will be upgraded to https://