static void validateHeaderConfigAction(String action) {
        if (HEADER_ACTIONS.stream().noneMatch(action::equalsIgnoreCase)) {
            throw new ConfigException(String.format("Invalid header config action: '%s'. "
                    + "Expected one of %s", action, HEADER_ACTIONS));
        }
    }
Add the properties related to an internal-only server to the given {@link ConfigDef}.
@param configDef the {@link ConfigDef} to add the properties to; may not be null
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/rest/RestServerConfig.java