如何在独立的阿波罗应用程序中使用安全WebSocket (WSS)？

const { createServer } = require('http');
const { ApolloServer } = require('apollo-server');
const { ApolloServerPluginDrainHttpServer } = require('apollo-server-core');
const { SubscriptionServer } = require('subscriptions-transport-ws');
const { execute, subscribe } = require('graphql');

const httpServer = createServer();
const server = new ApolloServer({ /* Apollo Server 配置 */ });

await server.start();

const subscriptionServer = SubscriptionServer.create(
  { /* Subscription Server 配置 */ },
  httpServer
);

await new Promise(resolve => httpServer.listen({ port: 4000 }, resolve));
console.log(`🚀 Server ready at http://localhost:4000${server.graphqlPath}`);
console.log(`🚀 Subscriptions ready at ws://localhost:4000${server.subscriptionsPath}`);

const { ApolloServerPluginDrainHttpServer } = require('apollo-server-core');
const { SubscriptionServer } = require('subscriptions-transport-ws');
const { execute, subscribe } = require('graphql');

const subscriptionServer = SubscriptionServer.create(
  {
    schema, // GraphQL schema
    execute,
    subscribe,
    /* 其他配置 */
  },
  {
    server: httpServer,
    path: server.subscriptionsPath,
  }
);

const fs = require('fs');
const https = require('https');

const options = {
  key: fs.readFileSync('path/to/private.key'),
  cert: fs.readFileSync('path/to/certificate.crt'),
  passphrase: 'certificate_password',
};

const httpServer = https.createServer(options);

const WebSocket = require('ws');

const client = new WebSocket('wss://localhost:4000/graphql');