private boolean isIpAddress(String candidate) {
        try {
            return new IPAddressString(candidate).isIPAddress();
        } catch (RuntimeException rte) {
            LOGGER.trace("Ignored error when parsing IP", rte);
            return false;
        }
    }
Seems it is common to support wildcards at only the start or end of the entry, so we'll do that for
now. If anyone wants wildcard support elsewhere they can ask for it.

We use Pattern.quote to make the rest of the string 'safe'.
gateway/platforms/vertx3/vertx3/src/main/java/io/apiman/gateway/platforms/vertx3/engine/proxy/JavaSysPropsProxySettings.java