Интеграция Stripe

Client ─→ POST /api/checkout
      ←─ Stripe Checkout URL
Client ─→ Stripe Checkout (hosted)
Stripe ─→ POST /api/webhook/stripe
       └→ обновить пользователя в DB

const session = await stripe.checkout.sessions.create({
  mode: 'subscription',
  line_items: [{ price: 'price_xxx', quantity: 1 }],
  customer_email: user.email,
  client_reference_id: user.id,
  success_url: `${SITE}/success?session_id={CHECKOUT_SESSION_ID}`,
  cancel_url: `${SITE}/pricing`,
  metadata: { user_id: user.id },
});
return { url: session.url };

const event = stripe.webhooks.constructEvent(
  rawBody, sig, WEBHOOK_SECRET
);

switch (event.type) {
  case 'checkout.session.completed':
    await activateSubscription(event.data.object);
  case 'invoice.payment_failed':
    await markAccountUnpaid(...);
  case 'customer.subscription.deleted':
    await deactivateSubscription(...);
}

const portal = await stripe.billingPortal.sessions.create({
  customer: customer.id,
  return_url: `${SITE}/account`,
});