`ctx.cookies`在apollo server-koa中始终是未定义的

const { ApolloServer } = require('apollo-server-koa');
const Koa = require('koa');

const typeDefs = `
  type Query {
    hello: String
  }
`;

const resolvers = {
  Query: {
    hello: () => 'Hello, world!',
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

const app = new Koa();

app.use(async (ctx, next) => {
  // 获取cookie
  const cookie = ctx.req.headers.cookie;
  console.log(cookie);

  // 设置cookie
  ctx.res.setHeader('Set-Cookie', 'name=value; Path=/;');

  await next();
});

server.applyMiddleware({ app });

app.listen({ port: 4000 }, () =>
  console.log(`Server ready at http://localhost:4000${server.graphqlPath}`)
);