// Receive events in real time
app.post('/nexus-hook', (req, res) => {
  const sig = req.headers['x-nexus-signature'];
  if (!verifyHMAC(sig, req.body)) 
    return res.sendStatus(401);

  const { event, data } = req.body;

  switch (event) {
    case 'message.received':
      crm.createLead({ phone: data.from });
      break;
    case 'campaign.completed':
      slack.notify(data.sent_count);
      break;
  }
  res.json({ received: true });
});