How to use the apollo-server-core.GraphQLExtension function in apollo-server-core

*
 * Copyright (c) 2019 MoleculerJS (https://github.com/moleculerjs/moleculer-apollo-server)
 * MIT Licensed
 */

"use strict";

const core = require("apollo-server-core");
const { ApolloServer } = require("./src/ApolloServer");
const ApolloService = require("./src/service");
const gql = require("./src/gql");

module.exports = {
	// Core
	GraphQLUpload: core.GraphQLUpload,
	GraphQLExtension: core.GraphQLExtension,
	gql: core.gql,
	ApolloError: core.ApolloError,
	toApolloError: core.toApolloError,
	SyntaxError: core.SyntaxError,
	ValidationError: core.ValidationError,
	AuthenticationError: core.AuthenticationError,
	ForbiddenError: core.ForbiddenError,
	UserInputError: core.UserInputError,
	defaultPlaygroundOptions: core.defaultPlaygroundOptions,

	// GraphQL tools
	...require("graphql-tools"),

	// Apollo Server
	ApolloServer,