class AttachmentAccessToken implements SignedExpiringToken {

    @Override
    public String getPayload() {
        return username
            + SEPARATOR
            + DateTimeFormatter.ISO_OFFSET_DATE_TIME.format(expirationDate);
    }

    @VisibleForTesting  AttachmentAccessToken(String username, String blobId, ZonedDateTime expirationDate, String signature);

}