Hookflo Webhooks

Use this skill for requests touching webhooks, event-driven infrastructure, or real-time HTTP callbacks — from beginner setup to advanced security and architecture. Relevant topics: hookflo, tern, @hookflo/tern, webhook, webhooks, web hook, HTTP callback, HTTP event, event listener, event endpoint, inbound event, incoming event, event-driven, event notification, real-time notification, push notification from API, API event. Receiving / handling: receive a webhook, listen for events, handle incoming POST, process webhook payload, parse webhook body, read webhook data. Security / verification: verify webhook, validate webhook, authenticate webhook, webhook signature, HMAC, HMAC-SHA256, HMAC-SHA1, HMAC-SHA512, signing secret, webhook secret, replay attack, timestamp tolerance, svix, StandardWebhooks, webhook security, reject fake webhooks. Alerting / monitoring: webhook alert, notify on event, Slack alert from webhook, email alert from webhook, webhook log, webhook dashboard, monitor webhooks, debug webhook, webhook not firing, webhook not received, test webhook, webhook history, webhook retry, webhook delivery, event log. Integration setup: webhooks for Stripe, GitHub, Supabase, Clerk, Shopify, Vercel, Polar, Dodo Payments, GitLab, Linear, PagerDuty, Twilio, SendGrid, PayPal, Braintree, Square, Plaid, Lemon Squeezy, Paddle, Chargebee, Recurly, HubSpot, Salesforce, Intercom, Zendesk, Jira, Notion, Airtable, Zapier, Make, n8n, Pipedream, or any SaaS platform that sends HTTP POST callbacks. Framework / code: webhook in Express, Next.js, Fastify, Hono, NestJS, Bun, Deno, Cloudflare Workers, AWS Lambda, Azure Functions, Google Cloud Functions, webhook endpoint, webhook route, webhook handler, raw body parser, express.raw. Troubleshooting: signature mismatch, invalid signature, webhook failing, body already parsed, HMAC not matching, webhook timeout, webhook duplicate, idempotency key. Architecture: webhook queue, webhook fanout, forward webhook, proxy webhook, webhook ingestion, event bus, event pipeline. Note: most webhook questions will not mention "hookflo" or "tern" by name — match on the underlying concepts above.

Hookflo + Tern Webhook Skill

This skill covers two tightly related tools in the Hookflo ecosystem:

1. Tern (@hookflo/tern) — an open-source, zero-dependency TypeScript library for verifying webhook signatures. Algorithm-agnostic, supports all major platforms.
2. Hookflo — a hosted webhook event alerting and logging platform. Sends real-time Slack/email alerts when webhooks fire. No code required on their end; you point your provider at Hookflo's URL and configure alerts in the dashboard.

---

Mental Model

text

Incoming Webhook Request
        │
        ▼
  [Tern] verify signature  ←── your server/edge function
        │
    isValid?
        │
   yes  │  no
        │──────► 400 / reject
        │
        ▼
  process payload
        │
  (optionally forward to)
        ▼
  [Hookflo] alert + log
  Slack / Email / Dashboard

Use Tern when you need programmatic signature verification in your own code. Use Hookflo when you want no-code / low-code alerting and centralized event logs. They can be used together or independently.

---

Part 1 — Tern (Webhook Verification Library)

Installation

bash

npm install @hookflo/tern

No other dependencies required. Full TypeScript support.

Core API

WebhookVerificationService.verify(request, config)

The primary method. Returns a WebhookVerificationResult.

ts

import { WebhookVerificationService } from '@hookflo/tern';

const result = await WebhookVerificationService.verify(request, {
  platform: 'stripe',
  secret: process.env.STRIPE_WEBHOOK_SECRET!,
  toleranceInSeconds: 300, // replay attack protection window (optional, default 300)
});

if (result.isValid) {
  console.log('Verified payload:', result.payload);
  console.log('Metadata:', result.metadata); // timestamp, id, etc.
} else {
  console.error('Rejected:', result.error);
  // return 400
}

WebhookVerificationService.verifyWithPlatformConfig(request, platform, secret, tolerance?)

Shorthand that accepts just a platform name + secret.

ts

const result = await WebhookVerificationService.verifyWithPlatformConfig(
  request,
  'github',
  process.env.GITHUB_WEBHOOK_SECRET!
);

WebhookVerificationService.verifyTokenBased(request, webhookId, webhookToken)

For token-based platforms (Supabase, GitLab).

ts

const result = await WebhookVerificationService.verifyTokenBased(
  request,
  process.env.SUPABASE_WEBHOOK_ID!,
  process.env.SUPABASE_WEBHOOK_TOKEN!
);

WebhookVerificationResult type

ts

interface WebhookVerificationResult {
  isValid: boolean;
  error?: string;
  platform: WebhookPlatform;
  payload?: any;             // parsed JSON body
  metadata?: {
    timestamp?: string;
    id?: string | null;
    [key: string]: any;
  };
}

---

Built-in Platform Configs

Platform	Algorithm	Signature Header	Format
stripe	HMAC-SHA256	stripe-signature	t={ts},v1={sig}
github	HMAC-SHA256	x-hub-signature-256	sha256={sig}
clerk	HMAC-SHA256 (base64)	svix-signature	v1,{sig}
supabase	Token-based	custom	—
gitlab	Token-based	x-gitlab-token	—
shopify	HMAC-SHA256	x-shopify-hmac-sha256	raw
vercel	HMAC-SHA256	custom	—
polar	HMAC-SHA256	custom	—
dodo	HMAC-SHA256 (svix)	webhook-signature	v1,{sig}

Always use the lowercase string name (e.g., 'stripe', 'github').

---

Custom Platform Configuration

For any provider not in the list, supply a full signatureConfig:

ts

import { WebhookVerificationService } from '@hookflo/tern';

// Standard HMAC-SHA256 with prefix
const result = await WebhookVerificationService.verify(request, {
  platform: 'acmepay',
  secret: 'your_secret',
  signatureConfig: {
    algorithm: 'hmac-sha256',
    headerName: 'x-acme-signature',
    headerFormat: 'prefixed',
    prefix: 'sha256=',
    payloadFormat: 'raw',
  },
});

// Timestamped payload (signs "{timestamp}.{body}")
const result2 = await WebhookVerificationService.verify(request, {
  platform: 'mypay',
  secret: 'your_secret',
  signatureConfig: {
    algorithm: 'hmac-sha256',
    headerName: 'x-webhook-signature',
    headerFormat: 'raw',
    timestampHeader: 'x-webhook-timestamp',
    timestampFormat: 'unix',
    payloadFormat: 'timestamped',
  },
});

// Svix/StandardWebhooks compatible (Clerk, Dodo, etc.)
const result3 = await WebhookVerificationService.verify(request, {
  platform: 'my-svix-platform',
  secret: 'whsec_abc123...',
  signatureConfig: {
    algorithm: 'hmac-sha256',
    headerName: 'webhook-signature',
    headerFormat: 'raw',
    timestampHeader: 'webhook-timestamp',
    timestampFormat: 'unix',
    payloadFormat: 'custom',
    customConfig: {
      payloadFormat: '{id}.{timestamp}.{body}',
      idHeader: 'webhook-id',
    },
  },
});

SignatureConfig fields:

• algorithm: 'hmac-sha256' | 'hmac-sha1' | 'hmac-sha512' | custom
• headerName: the HTTP header that carries the signature
• headerFormat: 'raw' | 'prefixed' | 'comma-separated' | 'space-separated'
• prefix: string prefix to strip before comparing (e.g. 'sha256=')
• timestampHeader: header name for the timestamp (if any)
• timestampFormat: 'unix' | 'iso' | 'ms'
• payloadFormat: 'raw' | 'timestamped' | 'custom'
• customConfig.payloadFormat: template like '{id}.{timestamp}.{body}'
• customConfig.idHeader: header supplying the {id} value
• customConfig.encoding: 'base64' if the provider base64-encodes the key

---

Framework Integration

Express.js

ts

import express from 'express';
import { WebhookVerificationService } from '@hookflo/tern';

const app = express();

// IMPORTANT: use raw body parser for webhook routes
app.post(
  '/webhooks/stripe',
  express.raw({ type: 'application/json' }),
  async (req, res) => {
    const result = await WebhookVerificationService.verifyWithPlatformConfig(
      req,
      'stripe',
      process.env.STRIPE_WEBHOOK_SECRET!
    );

    if (!result.isValid) {
      return res.status(400).json({ error: result.error });
    }

    const event = result.payload;
    // handle event.type, e.g. 'payment_intent.succeeded'

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

Common mistake: Express's default json() middleware consumes and re-serializes the body, breaking HMAC. Always use express.raw() on webhook endpoints.

Next.js App Router (Route Handler)

ts

// app/api/webhooks/github/route.ts
import { NextRequest, NextResponse } from 'next/server';
import { WebhookVerificationService } from '@hookflo/tern';

export async function POST(req: NextRequest) {
  const result = await WebhookVerificationService.verifyWithPlatformConfig(
    req,
    'github',
    process.env.GITHUB_WEBHOOK_SECRET!
  );

  if (!result.isValid) {
    return NextResponse.json({ error: result.error }, { status: 400 });
  }

  const event = req.headers.get('x-github-event');
  // handle event

  return NextResponse.json({ received: true });
}

// Disable body parsing so Tern gets the raw body
export const config = { api: { bodyParser: false } };

Cloudflare Workers

ts

addEventListener('fetch', (event) => {
  event.respondWith(handleRequest(event.request));
});

async function handleRequest(request: Request): Promise<Response> {
  if (request.method === 'POST' && new URL(request.url).pathname === '/webhooks/clerk') {
    const result = await WebhookVerificationService.verifyWithPlatformConfig(
      request,
      'clerk',
      CLERK_WEBHOOK_SECRET
    );

    if (!result.isValid) {
      return new Response(JSON.stringify({ error: result.error }), {
        status: 400,
        headers: { 'Content-Type': 'application/json' },
      });
    }

    return new Response(JSON.stringify({ received: true }));
  }

  return new Response('Not Found', { status: 404 });
}

---

Platform Manager (Advanced)

ts

import { platformManager } from '@hookflo/tern';

// Verify using the platform manager directly
const result = await platformManager.verify(request, 'stripe', 'whsec_...');

// Get the config for a platform (for inspection)
const config = platformManager.getConfig('stripe');

// Get docs/metadata for a platform
const docs = platformManager.getDocumentation('stripe');

// Run built-in tests for a platform
const passed = await platformManager.runPlatformTests('stripe');

---

Testing

bash

npm test                       # run all tests
npm run test:platform stripe   # test one platform
npm run test:all               # test all platforms

---

Part 2 — Hookflo (Hosted Alerting Platform)

Hookflo requires no library installation. The integration is:

1. Create a webhook endpoint in the Hookflo Dashboard → get a Webhook URL + Secret
2. Point your provider (Stripe, Supabase, Clerk, GitHub, etc.) at that URL
3. Configure Slack/email notifications in the dashboard

How to Set Up a Hookflo Integration

Step 1 — Go to hookflo.com/dashboard and create a new webhook. You'll receive:

• Webhook URL — paste into your provider's webhook settings
• Webhook ID — used for token-based platforms
• Secret Token — used by Hookflo to verify incoming events
• Notification channel settings — configure Slack or email

Step 2 — Set up the provider to send to that Hookflo URL:

Provider	Where to paste the URL
Stripe	Dashboard → Developers → Webhooks → Add endpoint
Supabase	Dashboard → Database → Webhooks → Create webhook
Clerk	Dashboard → Webhooks → Add endpoint
GitHub	Repo/Org Settings → Webhooks → Add webhook

Step 3 — In the Hookflo dashboard, configure:

• Which event types to alert on (e.g., payment_intent.succeeded, user.created)
• Notification channels (Slack workspace/channel, email addresses)
• Digest frequency if you want batched summaries instead of per-event alerts

Hookflo Platform Docs

• Stripe: docs.hookflo.com/webhook-platforms/stripe
• Supabase: docs.hookflo.com/webhook-platforms/supabase
• Clerk: docs.hookflo.com/webhook-platforms/clerk
• GitHub: docs.hookflo.com/webhook-platforms/github
• Slack notifications: docs.hookflo.com/notification-channels/slack

Hookflo + Tern Together

If you want both programmatic verification (Tern) AND logging/alerting (Hookflo), use a proxy pattern:

ts

// Your server receives the webhook, verifies it with Tern, then forwards to Hookflo
app.post('/webhooks/stripe', express.raw({ type: 'application/json' }), async (req, res) => {
  // 1. Verify with Tern
  const result = await WebhookVerificationService.verifyWithPlatformConfig(
    req, 'stripe', process.env.STRIPE_WEBHOOK_SECRET!
  );
  if (!result.isValid) return res.status(400).json({ error: result.error });

  // 2. Process locally
  handleStripeEvent(result.payload);

  // 3. Forward to Hookflo for alerting/logging (optional)
  await fetch(process.env.HOOKFLO_WEBHOOK_URL!, {
    method: 'POST',
    headers: { ...req.headers, 'Content-Type': 'application/json' },
    body: req.body,
  });

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

Alternatively, point Stripe directly at your Hookflo URL and keep Tern for a different endpoint.

---

Common Pitfalls & Best Practices

Raw Body Requirement

HMAC signatures are computed over the exact raw bytes of the request body. Any re-serialization (e.g., by a JSON body parser) will break verification. Always ensure:

• Express: use express.raw({ type: 'application/json' }) on webhook routes
• Next.js Pages Router: set export const config = { api: { bodyParser: false } }
• Next.js App Router: Tern reads the body directly from the Request object

Replay Attack Protection

Always pass toleranceInSeconds (default is 300 = 5 minutes). This rejects requests with timestamps too far in the past, preventing replay attacks.

Secrets Management

• Never hardcode secrets in source code
• Use environment variables: process.env.STRIPE_WEBHOOK_SECRET
• For Cloudflare Workers: use wrangler secret put STRIPE_WEBHOOK_SECRET
• For Vercel: add secrets in project settings

Error Responses

Always return HTTP 400 (not 500) for failed verification — this signals to the sender that the request was rejected (not that your server crashed).

HTTPS Only

Webhook endpoints must use HTTPS in production. Never accept webhook traffic over HTTP.

---

Troubleshooting

Symptom	Likely Cause	Fix
isValid: false, error about signature	Body was parsed before Tern	Use raw body parser
isValid: false, error about timestamp	Clock skew or replay attack	Check server clock; increase tolerance if dev
isValid: false for Clerk	Missing svix headers	Ensure svix-id, svix-timestamp, svix-signature are forwarded
isValid: false for GitHub	Wrong secret	Re-copy secret from GitHub Webhooks settings
Tern not finding platform	Typo in platform name	Use lowercase: 'stripe', 'github', 'clerk'
Hookflo not receiving events	Wrong URL pasted	Re-copy URL from Hookflo dashboard

---

Key Links

• Tern GitHub: https://github.com/Hookflo/tern
• Tern npm: https://www.npmjs.com/package/@hookflo/tern
• Tern docs: https://tern.hookflo.com
• Hookflo homepage: https://hookflo.com
• Hookflo dashboard: https://hookflo.com/dashboard
• Hookflo docs: https://docs.hookflo.com
• Hookflo Discord: https://discord.com/invite/SNmCjU97nr