Billing is solved. Enforcement isn't.

1// 1. Listen for subscription changes
2app.post('/webhooks/stripe', async (req, res) => {
3  const event = stripe.webhooks.constructEvent(
4    req.body, sig, secret
5  );
6
7  if (event.type === 'customer.subscription.updated') {
8    const sub = event.data.object;
9    const plan = await db.plans.findByStripePriceId(
10      sub.items[0].price.id
11    );
12    await db.entitlements.upsert({
13      customerId: sub.customer,
14      planId: plan.id,
15      features: plan.features,
16      limits: plan.limits,
17    });
18    await redis.del(`entitlements:${sub.customer}`);
19  }
20});
21
22// 2. Check entitlements on every request
23async function checkAccess(customerId, feature) {
24  let ent = await redis.get(
25    `entitlements:${customerId}`
26  );
27  if (!ent) {
28    ent = await db.entitlements.findByCustomer(
29      customerId
30    );
31    await redis.set(
32      `entitlements:${customerId}`, ent, 'EX', 300
33    );
34  }
35  const limit = ent.limits[feature];
36  const usage = await db.usage.count({
37    customerId, feature, period: 'month'
38  });
39  return usage < limit;
40}
41
42// 3. Track usage and sync to Stripe
43async function trackUsage(customerId, feature) {
44  await db.usage.insert({
45    customerId, feature, timestamp: Date.now()
46  });
47  const meterId = await db.meters.findByFeature(
48    feature
49  );
50  await stripe.billing.meterEvents.create({
51    event_name: meterId,
52    payload: {
53      stripe_customer_id: customerId,
54      value: '1',
55    },
56  });
57}
58
59// 4. Handle overrides, trials, custom plans...
60// (another 200 lines)