private static String key(String userId, OffsetDateTime createdOn) {
        return String.join("-", userId, createdOn.toString()); // TODO(msavy): userId alone might be good enough?
    }
@author Marc Savy {@literal <marc@blackparrotlabs.io>}
manager/api/rest-impl/src/main/java/io/apiman/manager/api/service/SsoEventService.java