// Simplified Stripe Checkout flow
const stripe = await loadStripe('pk_test_...');
const session = await stripe.checkout.sessions.create({
  payment_method_types: ['card'],
  line_items: [{
    price: 'price_premium_yearly',
    quantity: 1,
  }],
  mode: 'subscription',
  success_url: 'https://yoursite.com/success?session_id={CHECKOUT_SESSION_ID}',
  cancel_url: 'https://yoursite.com/cancel',
});
stripe.redirectToCheckout({ sessionId: session.id });

// Backend (Node.js example)
app.post('/api/validate-license', async (req, res) => {
  const { licenseKey } = req.body;
  
  // Rate limiting check
  if (await isRateLimited(req.ip)) {
    return res.status(429).json({ error: 'Too many requests' });
  }
  
  const license = await db.licenses.findOne({ key: licenseKey });
  
  if (!license) {
    return res.status(401).json({ valid: false, error: 'Invalid license' });
  }
  
  if (license.expiresAt && new Date() > license.expiresAt) {
    return res.status(401).json({ valid: false, error: 'License expired' });
  }
  
  // Return validated status with metadata
  res.json({ 
    valid: true, 
    plan: license.plan,
    features: license.features,
    expiresAt: license.expiresAt
  });
});