@Override
        public String lookup(String key) {
            // Upside of this approach is that we can capture any dynamically defined variables.
            // Downside is that it's slightly expensive but should only happen at startup.
            Map<String, String> flattenedMap = new LinkedHashMap<>();
            jsonMapToProperties("", new JsonObject(getVariables().encode()), flattenedMap);
            if (flattenedMap.containsKey(key)) {
                return flattenedMap.get(key);
            } else {
                return super.lookup(key);
            }
        }
Gets all properties in the engine configuration that are prefixed
with the given prefix.
@param prefix the prefix
@return all prefixed properties
gateway/platforms/vertx3/vertx3/src/main/java/io/apiman/gateway/platforms/vertx3/common/config/VertxEngineConfig.java