@Override
        public String toString() {
            return new StringJoiner(", ", MatchCacheKey.class.getSimpleName() + "[", "]")
                    .add("config=" + config)
                    .add("addr='" + addr + "'")
                    .toString();
        }
Cache key consisting of configuration and address, which should uniquely identify a policy + IP being operated upon.
<p>
{@link IPListConfig} is immutable and caches <code>hashCode</code> in order to avoid expensive re-hashing of the IP list (which could be very long).
gateway/engine/policies/src/main/java/io/apiman/gateway/engine/policies/AbstractIPListPolicy.java