---

name: payment-gateway-integration description: Integrates payment processing with Stripe, PayPal, or Square including subscriptions, webhooks, and PCI compliance. Use when implementing checkout flows, recurring billing, or handling refunds and disputes.

Payment Gateway Integration

Integrate secure payment processing with proper error handling and compliance.

Stripe Integration (Node.js)

const stripe = require('stripe')(process.env.STRIPE_SECRET_KEY);

class PaymentService {
  async createPaymentIntent(amount, currency, customerId) {
    return stripe.paymentIntents.create({
      amount: Math.round(amount * 100), // Convert to cents
      currency,
      customer: customerId,
      automatic_payment_methods: { enabled: true }
    });
  }

  async createSubscription(customerId, priceId) {
    return stripe.subscriptions.create({
      customer: customerId,
      items: [{ price: priceId }],
      payment_behavior: 'default_incomplete',
      expand: ['latest_invoice.payment_intent']
    });
  }

  async refund(paymentIntentId, amount = null) {
    const params = { payment_intent: paymentIntentId };
    if (amount) params.amount = Math.round(amount * 100);
    return stripe.refunds.create(params);
  }
}

Webhook Handling

app.post('/webhooks/stripe', express.raw({ type: 'application/json' }), (req, res) => {
  const sig = req.headers['stripe-signature'];

  let event;
  try {
    event = stripe.webhooks.constructEvent(req.body, sig, process.env.STRIPE_WEBHOOK_SECRET);
  } catch (err) {
    return res.status(400).send(`Webhook Error: ${err.message}`);
  }

  switch (event.type) {
    case 'payment_intent.succeeded':
      await handlePaymentSuccess(event.data.object);
      break;
    case 'invoice.payment_failed':
      await handlePaymentFailed(event.data.object);
      break;
  }

  res.json({ received: true });
});

PayPal Integration

See references/paypal-integration.md for complete PayPal implementation with:

• Order creation and capture
• Refund processing
• Webhook handling
• Frontend SDK integration
• Success/cancel callbacks

Security Checklist

• Use official SDK only
• Verify webhook signatures
• Never log full card numbers
• Store minimal payment data
• Test in sandbox first
• HTTPS for all payment routes
• Handle all error cases
• Use idempotency keys
• Implement retry logic

Best Practices

Do:

• Use official SDK libraries
• Verify all webhook signatures
• Log transaction IDs (not card data)
• Test in sandbox environment
• Handle all payment states
• Implement proper error messages

Don't:

• Process raw card data directly
• Store sensitive payment info
• Hardcode API keys
• Skip webhook signature validation
• Ignore failed payment events
• Use test keys in production