func parseSANExtension(der cryptobyte.String) (dnsNames, emailAddresses []string, ipAddresses []net.IP, uris []*url.URL, err error) {
	err = forEachSAN(der, func(tag int, data []byte) error {
		switch tag {
		case nameTypeEmail:
			email := string(data)
			if err := isIA5String(email); err != nil {
				return errors.New("x509: SAN rfc822Name is malformed")
			}
			emailAddresses = append(emailAddresses, email)
		case nameTypeDNS:

				return nil, fmt.Errorf("cannot parse invalid IP: %s", err)
			}
			template.IPAddresses = append(template.IPAddresses, net.IP(ipBytes))

		case strings.HasPrefix(name, "email:"):
			template.EmailAddresses = append(template.EmailAddresses, name[6:])

		case strings.HasPrefix(name, "uri:"):
			uri, err := url.Parse(name[4:])
			if err != nil {
				return nil, fmt.Errorf("cannot parse URI %q: %s", name[4:], err)
			}