Обработка вебхуков GitHub: timing-safe HMAC и дедупликация доставок

import { createHmac, timingSafeEqual } from 'node:crypto';

export async function handler(event) {
  const body = event.body ?? '';
  const sigHeader = (event.headers['x-hub-signature-256'] ?? '').replace('sha256=', '');
  const expected = createHmac('sha256', process.env.GITHUB_WEBHOOK_SECRET).update(body).digest('hex');
  if (sigHeader.length !== expected.length ||
      !timingSafeEqual(Buffer.from(sigHeader, 'hex'), Buffer.from(expected, 'hex'))) {
    return { statusCode: 401, body: 'invalid signature' };
  }
  const eventType = event.headers['x-github-event'];
  const deliveryId = event.headers['x-github-delivery'];
  const payload = JSON.parse(body);
  const isNew = await db.webhookDeliveries.upsert(deliveryId);
  if (!isNew) return { statusCode: 200, body: 'duplicate' };
  if (eventType === 'push') {
    await global.durable.startNew('index-repo', undefined, { repo: payload.repository.full_name, sha: payload.after });
  } else if (eventType === 'pull_request' && payload.action === 'opened') {
    await global.durable.startNew('review-pr', undefined, { repo: payload.repository.full_name, pr: payload.number });
  } else if (eventType === 'release' && payload.action === 'published') {
    await global.durable.startNew('deploy-release', undefined, { repo: payload.repository.full_name, tag: payload.release.tag_name });
  }
  return { statusCode: 200, body: 'accepted' };
}