I'm trying to create a login system with GraphQL and Express, but the sessions aren't being saved. Whenever I log in, req.session.userId stays undefined.

My code:

(async () => {
    await connect(process.env.MONGO_URI!, { dbName: "example" });

    const app = express();

    app.use(
        cors({
            origin: [__clientUrl__, "https://studio.apollographql.com"],
            credentials: true
        })
    );

    app.use(
        session({
            name: "qid",
            secret: process.env.SESSION_SECRET!,
            store: MongoStore.create({
                mongoUrl: process.env.MONGO_URI,
                dbName: "example"
            }),
            saveUninitialized: false,
            resave: false,
            cookie: {
                maxAge: 6.048e8,
                httpOnly: __prod__,
                sameSite: "lax",
                secure: __prod__
            }
        })
    );

    const server = new ApolloServer({
        schema: await buildSchema({
            resolvers: [HelloResolver, UserResolver],
            validate: false
        }),
        context: ({ req, res }) => ({ req, res })
    });

    await server.start();

    server.applyMiddleware({
        app,
        cors: {
            origin: [__clientUrl__, "https://studio.apollographql.com"],
            credentials: true
        }
    });

    app.listen(__port__, () =>
        console.log(
            `