Subscribing and verifying webhooks

import express from 'express';
import crypto from 'crypto';

const app = express();
const SECRET = process.env.CATIVA_WEBHOOK_SECRET; // whsec_...

app.post(
  '/webhooks/cativa',
  express.raw({ type: 'application/json' }),
  (req, res) => {
    const header = req.header('X-Cativa-Signature') ?? '';
    const parts = Object.fromEntries(
      header.split(',').map(p => p.split('='))
    );
    const ts = Number(parts.t);
    const sig = parts.v1;

    if (!ts || !sig) return res.status(400).send('bad signature header');
    if (Math.abs(Date.now() / 1000 - ts) > 300) {
      return res.status(400).send('stale timestamp');
    }

    const expected = crypto
      .createHmac('sha256', SECRET)
      .update(`${ts}.${req.body.toString('utf8')}`)
      .digest('hex');

    const ok = crypto.timingSafeEqual(
      Buffer.from(expected, 'hex'),
      Buffer.from(sig, 'hex')
    );
    if (!ok) return res.status(401).send('invalid signature');

    const event = JSON.parse(req.body.toString('utf8'));
    // ... process the event
    res.status(200).send('ok');
  }
);

import hmac
import hashlib
import os
import time
from flask import Flask, request, abort

app = Flask(__name__)
SECRET = os.environ['CATIVA_WEBHOOK_SECRET'].encode()  # whsec_...

@app.post('/webhooks/cativa')
def receive():
    header = request.headers.get('X-Cativa-Signature', '')
    parts = dict(p.split('=', 1) for p in header.split(',') if '=' in p)
    try:
        ts = int(parts['t'])
        sig = parts['v1']
    except (KeyError, ValueError):
        abort(400, 'bad signature header')

    if abs(time.time() - ts) > 300:
        abort(400, 'stale timestamp')

    raw_body = request.get_data()  # raw bytes — do not use request.json
    expected = hmac.new(
        SECRET,
        f"{ts}.".encode() + raw_body,
        hashlib.sha256
    ).hexdigest()

    if not hmac.compare_digest(expected, sig):
        abort(401, 'invalid signature')

    payload = request.get_json()
    # ... process the event
    return ('ok', 200)

package main

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

var secret = []byte(os.Getenv("CATIVA_WEBHOOK_SECRET")) // whsec_...

func handleWebhook(w http.ResponseWriter, r *http.Request) {
    body, err := io.ReadAll(r.Body)
    if err != nil {
        http.Error(w, "read body", http.StatusBadRequest)
        return
    }

    var ts int64
    var sig string
    for _, part := range strings.Split(r.Header.Get("X-Cativa-Signature"), ",") {
        kv := strings.SplitN(part, "=", 2)
        if len(kv) != 2 {
            continue
        }
        switch kv[0] {
        case "t":
            ts, _ = strconv.ParseInt(kv[1], 10, 64)
        case "v1":
            sig = kv[1]
        }
    }
    if ts == 0 || sig == "" {
        http.Error(w, "bad signature header", http.StatusBadRequest)
        return
    }

    if abs(time.Now().Unix()-ts) > 300 {
        http.Error(w, "stale timestamp", http.StatusBadRequest)
        return
    }

    mac := hmac.New(sha256.New, secret)
    mac.Write([]byte(strconv.FormatInt(ts, 10) + "."))
    mac.Write(body)
    expected := hex.EncodeToString(mac.Sum(nil))

    if !hmac.Equal([]byte(expected), []byte(sig)) {
        http.Error(w, "invalid signature", http.StatusUnauthorized)
        return
    }

    // ... process the event using body
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("ok"))
}

func abs(x int64) int64 {
    if x < 0 {
        return -x
    }
    return x
}

using System.Globalization;
using System.Security.Cryptography;
using System.Text;

app.MapPost("/webhooks/cativa", async (HttpContext ctx) =>
{
    var secret = Encoding.UTF8.GetBytes(
        Environment.GetEnvironmentVariable("CATIVA_WEBHOOK_SECRET")!); // whsec_...

    using var ms = new MemoryStream();
    await ctx.Request.Body.CopyToAsync(ms);
    var rawBody = ms.ToArray();

    var header = ctx.Request.Headers["X-Cativa-Signature"].ToString();
    long ts = 0;
    string? sig = null;
    foreach (var part in header.Split(','))
    {
        var kv = part.Split('=', 2);
        if (kv.Length != 2) continue;
        if (kv[0] == "t") long.TryParse(kv[1], NumberStyles.Integer, CultureInfo.InvariantCulture, out ts);
        else if (kv[0] == "v1") sig = kv[1];
    }

    if (ts == 0 || sig is null)
        return Results.BadRequest("bad signature header");

    var nowUnix = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
    if (Math.Abs(nowUnix - ts) > 300)
        return Results.BadRequest("stale timestamp");

    using var hmac = new HMACSHA256(secret);
    var data = Encoding.UTF8.GetBytes($"{ts}.").Concat(rawBody).ToArray();
    var expected = Convert.ToHexString(hmac.ComputeHash(data)).ToLowerInvariant();

    var expectedBytes = Encoding.UTF8.GetBytes(expected);
    var sigBytes = Encoding.UTF8.GetBytes(sig);
    if (expectedBytes.Length != sigBytes.Length ||
        !CryptographicOperations.FixedTimeEquals(expectedBytes, sigBytes))
        return Results.Unauthorized();

    // ... process the event using rawBody
    return Results.Ok("ok");
});