How Paddle Billing signs webhooks

const crypto = require('node:crypto');

const TOLERANCE_SECONDS = 5;

/**
 * Verify a Paddle Billing webhook. rawBody: the request body as a Buffer, exactly as received
 * (before any JSON parsing); headers: lower-case names, as in req.headers.
 */
function verifyWebhook(rawBody, headers, secret, url = '', method = 'POST') {
  rawBody = Buffer.from(rawBody);
  const header = headers['paddle-signature'] || '';
  const pairs = header.split(';').map((part) => part.trim().split('='));
  const ts = pairs.find(([k]) => k === 'ts')?.[1] || '';
  const signatures = pairs.filter(([k]) => k === 'h1').map(([, v]) => v);
  const signed = Buffer.concat([Buffer.from(ts + ':'), rawBody]);
  const key = secret;
  const expected = crypto.createHmac('sha256', key).update(signed).digest('hex');
  const valid = signatures.some((sig) => {
    const a = Buffer.from(sig.toLowerCase());
    const b = Buffer.from(expected);
    return a.length === b.length && crypto.timingSafeEqual(a, b);
  });
  if (!valid) return false;
  const signedAt = Number(ts);
  return Number.isFinite(signedAt) && Math.abs(Date.now() / 1000 - signedAt) <= TOLERANCE_SECONDS;
}

// Express: keep the raw body for this route
// app.post('/webhooks/paddle', express.raw({ type: '*/*' }), (req, res) => {
//   if (!verifyWebhook(req.body, req.headers, process.env.PADDLE_WEBHOOK_SECRET)) return res.sendStatus(401);
//   res.sendStatus(200); // then process the event asynchronously
// });

import base64
import hashlib
import hmac
import time

TOLERANCE_SECONDS = 5


def verify_webhook(raw_body: bytes, headers, secret: str, url: str = '', method: str = 'POST') -> bool:
    """Verify a Paddle Billing webhook. raw_body: the request body exactly as received (bytes);
    headers: a mapping with lower-case names (Flask and Django headers are case-insensitive)."""
    header = headers.get('paddle-signature', '')
    pairs = [part.strip().split('=', 1) for part in header.split(';')]
    ts = next((p[1] for p in pairs if len(p) == 2 and p[0] == 'ts'), '')
    signatures = [p[1] for p in pairs if len(p) == 2 and p[0] == 'h1']
    signed = (ts + ':').encode() + raw_body
    key = secret.encode()
    digest = hmac.new(key, signed, hashlib.sha256).digest()
    expected = digest.hex()
    if not any(hmac.compare_digest(sig.lower(), expected) for sig in signatures):
        return False
    try:
        signed_at = int(ts)
    except ValueError:
        return False
    return abs(time.time() - signed_at) <= TOLERANCE_SECONDS


# Flask: verify_webhook(request.get_data(), request.headers, SECRET)

<?php

const TOLERANCE_SECONDS = 5;

/**
 * Verify a Paddle Billing webhook. $rawBody: file_get_contents('php://input'), before any decoding;
 * $headers: lower-case names, e.g. array_change_key_case(getallheaders()).
 */
function verify_webhook(string $rawBody, array $headers, string $secret, string $url = '', string $method = 'POST'): bool
{
    $header = (string) ($headers['paddle-signature'] ?? '');
    $ts = '';
    $signatures = [];
    foreach (explode(';', $header) as $part) {
        [$k, $v] = array_pad(explode('=', trim($part), 2), 2, '');
        if ($k === 'ts') {
            $ts = $v;
        } elseif ($k === 'h1') {
            $signatures[] = $v;
        }
    }
    $signed = $ts . ':' . $rawBody;
    $key = $secret;
    $expected = hash_hmac('sha256', $signed, $key);
    $valid = false;
    foreach ($signatures as $sig) {
        $valid = $valid || hash_equals($expected, strtolower($sig));
    }
    if (! $valid) {
        return false;
    }
    $signedAt = (int) $ts;

    return $signedAt > 0 && abs(time() - $signedAt) <= TOLERANCE_SECONDS;
}

package webhooks

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"math"
	"net/http"
	"strconv"
	"strings"
	"time"
)

const toleranceSeconds = 5

// VerifyWebhook checks a Paddle Billing webhook. rawBody is the request body exactly as received
// (io.ReadAll(r.Body) before any decoding).
func VerifyWebhook(rawBody []byte, h http.Header, secret, url, method string) bool {
	header := h.Get("Paddle-Signature")
	ts := ""
	var signatures []string
	for _, part := range strings.Split(header, ";") {
		k, v, _ := strings.Cut(strings.TrimSpace(part), "=")
		switch k {
		case "ts":
			ts = v
		case "h1":
			signatures = append(signatures, v)
		}
	}
	signed := []byte{}
	signed = append(signed, ts...)
	signed = append(signed, ":"...)
	signed = append(signed, rawBody...)
	key := []byte(secret)
	mac := hmac.New(sha256.New, key)
	mac.Write(signed)
	expected := hex.EncodeToString(mac.Sum(nil))
	valid := false
	for _, sig := range signatures {
		if hmac.Equal([]byte(strings.ToLower(sig)), []byte(expected)) {
			valid = true
		}
	}
	if !valid {
		return false
	}
	n, err := strconv.ParseFloat(ts, 64)
	if err != nil {
		return false
	}
	signedAt := n
	return math.Abs(float64(time.Now().Unix())-signedAt) <= toleranceSeconds
}