OpenAI Webhooks Skill

When to Use This Skill

• Setting up OpenAI webhook handlers for async operations
• Debugging signature verification failures
• Handling fine-tuning job completion events
• Processing batch API completion notifications
• Handling realtime API incoming calls

Essential Code (USE THIS)

Express Webhook Handler

const express = require('express');
const crypto = require('crypto');

const app = express();

// Standard Webhooks signature verification for OpenAI
function verifyOpenAISignature(payload, webhookId, webhookTimestamp, webhookSignature, secret) {
  if (!webhookSignature || !webhookSignature.includes(',')) {
    return false;
  }

  // Check timestamp is within 5 minutes to prevent replay attacks
  const currentTime = Math.floor(Date.now() / 1000);
  const timestampDiff = currentTime - parseInt(webhookTimestamp);
  if (timestampDiff > 300 || timestampDiff < -300) {
    console.error('Webhook timestamp too old or too far in the future');
    return false;
  }

  // Extract version and signature
  const [version, signature] = webhookSignature.split(',');
  if (version !== 'v1') {
    return false;
  }

  // Create signed content: webhook_id.webhook_timestamp.payload
  const payloadStr = payload instanceof Buffer ? payload.toString('utf8') : payload;
  const signedContent = `${webhookId}.${webhookTimestamp}.${payloadStr}`;

  // Decode base64 secret (remove whsec_ prefix if present)
  const secretKey = secret.startsWith('whsec_') ? secret.slice(6) : secret;
  const secretBytes = Buffer.from(secretKey, 'base64');

  // Generate expected signature
  const expectedSignature = crypto
    .createHmac('sha256', secretBytes)
    .update(signedContent, 'utf8')
    .digest('base64');

  // Timing-safe comparison
  return crypto.timingSafeEqual(
    Buffer.from(signature),
    Buffer.from(expectedSignature)
  );
}

// CRITICAL: Use express.raw() for webhook endpoint - OpenAI needs raw body
app.post('/webhooks/openai',
  express.raw({ type: 'application/json' }),
  async (req, res) => {
    const webhookId = req.headers['webhook-id'];
    const webhookTimestamp = req.headers['webhook-timestamp'];
    const webhookSignature = req.headers['webhook-signature'];

    // Verify signature
    if (!verifyOpenAISignature(
      req.body,
      webhookId,
      webhookTimestamp,
      webhookSignature,
      process.env.OPENAI_WEBHOOK_SECRET
    )) {
      console.error('Invalid OpenAI webhook signature');
      return res.status(400).send('Invalid signature');
    }

    // Parse the verified payload
    const event = JSON.parse(req.body.toString());

    // Handle the event
    switch (event.type) {
      case 'fine_tuning.job.succeeded':
        console.log('Fine-tuning job succeeded:', event.data.id);
        break;
      case 'fine_tuning.job.failed':
        console.log('Fine-tuning job failed:', event.data.id);
        break;
      case 'batch.completed':
        console.log('Batch completed:', event.data.id);
        break;
      case 'batch.failed':
        console.log('Batch failed:', event.data.id);
        break;
      case 'batch.cancelled':
        console.log('Batch cancelled:', event.data.id);
        break;
      case 'batch.expired':
        console.log('Batch expired:', event.data.id);
        break;
      case 'realtime.call.incoming':
        console.log('Realtime call incoming:', event.data.id);
        break;
      default:
        console.log('Unhandled event:', event.type);
    }

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

Python (FastAPI) Webhook Handler

import os
import hmac
import hashlib
import base64
import time
from fastapi import FastAPI, Request, HTTPException, Header

app = FastAPI()

def verify_openai_signature(
    payload: bytes,
    webhook_id: str,
    webhook_timestamp: str,
    webhook_signature: str,
    secret: str
) -> bool:
    if not webhook_signature or ',' not in webhook_signature:
        return False

    # Check timestamp is within 5 minutes
    current_time = int(time.time())
    timestamp_diff = current_time - int(webhook_timestamp)
    if timestamp_diff > 300 or timestamp_diff < -300:
        return False

    # Extract version and signature
    version, signature = webhook_signature.split(',', 1)
    if version != 'v1':
        return False

    # Create signed content
    signed_content = f"{webhook_id}.{webhook_timestamp}.{payload.decode('utf-8')}"

    # Decode base64 secret (remove whsec_ prefix if present)
    secret_key = secret[6:] if secret.startswith('whsec_') else secret
    secret_bytes = base64.b64decode(secret_key)

    # Generate expected signature
    expected_signature = base64.b64encode(
        hmac.new(
            secret_bytes,
            signed_content.encode('utf-8'),
            hashlib.sha256
        ).digest()
    ).decode('utf-8')

    return hmac.compare_digest(signature, expected_signature)

@app.post("/webhooks/openai")
async def openai_webhook(
    request: Request,
    webhook_id: str = Header(None, alias="webhook-id"),
    webhook_timestamp: str = Header(None, alias="webhook-timestamp"),
    webhook_signature: str = Header(None, alias="webhook-signature")
):
    payload = await request.body()

    # Verify signature
    if not verify_openai_signature(
        payload,
        webhook_id,
        webhook_timestamp,
        webhook_signature,
        os.environ.get("OPENAI_WEBHOOK_SECRET")
    ):
        raise HTTPException(status_code=400, detail="Invalid signature")

    # Parse and handle event
    event = await request.json()

    # Handle event...
    return {"received": True}

For complete working examples with tests, see:

• examples/express/ - Full Express implementation
• examples/nextjs/ - Next.js App Router implementation
• examples/fastapi/ - Python FastAPI implementation

Common Event Types

For full event reference, see OpenAI Webhook Events

Environment Variables

OPENAI_API_KEY=sk-xxxxx          # Your OpenAI API key
OPENAI_WEBHOOK_SECRET=whsec_xxxxx # Your webhook signing secret

Local Development

# Start tunnel (no account needed)
npx hookdeck-cli listen 3000 openai --path /webhooks/openai

Reference Materials

• references/overview.md - OpenAI webhook concepts
• references/setup.md - Dashboard configuration
• references/verification.md - Signature verification details