Webhooks

# Shell (OpenSSL) — for debugging a captured delivery. In production verify in your application code: this
# comparison is not constant-time.
# Usage: verify_signature "$X_LMS_SIGNATURE" body.json "$WEBHOOK_SECRET" [now]
verify_signature() {
  local header="$1" body_file="$2" secret="$3" now="${4:-$(date +%s)}"
  local timestamp="" expected part
  for part in ${header//,/ }; do
    case "$part" in t=*) timestamp="${part#t=}" ;; esac
  done
  case "$timestamp" in ''|*[!0-9]*) return 1 ;; esac
  local age=$((now - timestamp))
  [ "${age#-}" -le 300 ] || return 1
  expected=$( { printf '%s.' "$timestamp"; cat "$body_file"; } | openssl dgst -sha256 -hmac "$secret" -r | cut -d' ' -f1)
  for part in ${header//,/ }; do
    [ "$part" = "v1=$expected" ] && return 0
  done
  return 1
}

import hashlib
import hmac
import time


def verify_signature(header: str, raw_body: bytes, secret: str, tolerance: int = 300, now: float | None = None) -> bool:
    """Checks X-LMS-Signature: t={timestamp},v1={hex}[,v1={hex}] against the raw request body."""
    timestamp, signatures = None, []
    for part in header.split(","):
        key, _, value = part.strip().partition("=")
        if key == "t" and value.isdigit():
            timestamp = int(value)
        elif key == "v1":
            signatures.append(value)
    if timestamp is None or not signatures:
        return False
    if abs((time.time() if now is None else now) - timestamp) > tolerance:
        return False
    expected = hmac.new(secret.encode(), f"{timestamp}.".encode() + raw_body, hashlib.sha256).hexdigest()
    return any(hmac.compare_digest(expected, signature) for signature in signatures)


# Flask: verify_signature(request.headers["X-LMS-Signature"], request.get_data(), WEBHOOK_SECRET)

<?php

/** Checks X-LMS-Signature: t={timestamp},v1={hex}[,v1={hex}] against the raw request body. */
function verify_signature(string $header, string $rawBody, string $secret, int $tolerance = 300, ?int $now = null): bool
{
    $timestamp = null;
    $signatures = [];
    foreach (explode(',', $header) as $part) {
        [$key, $value] = array_pad(explode('=', trim($part), 2), 2, '');
        if ($key === 't' && ctype_digit($value)) {
            $timestamp = (int) $value;
        } elseif ($key === 'v1') {
            $signatures[] = $value;
        }
    }
    if ($timestamp === null || $signatures === []) {
        return false;
    }
    if (abs(($now ?? time()) - $timestamp) > $tolerance) {
        return false;
    }
    $expected = hash_hmac('sha256', $timestamp . '.' . $rawBody, $secret);
    foreach ($signatures as $signature) {
        if (hash_equals($expected, $signature)) {
            return true;
        }
    }
    return false;
}

// verify_signature($_SERVER['HTTP_X_LMS_SIGNATURE'] ?? '', file_get_contents('php://input'), $webhookSecret);

package main

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

// VerifySignature checks X-LMS-Signature: t={timestamp},v1={hex}[,v1={hex}] against the raw request body.
func VerifySignature(header string, rawBody []byte, secret string, tolerance time.Duration, now time.Time) bool {
	var timestamp int64 = -1
	var signatures [][]byte
	for _, part := range strings.Split(header, ",") {
		key, value, _ := strings.Cut(strings.TrimSpace(part), "=")
		switch key {
		case "t":
			if t, err := strconv.ParseInt(value, 10, 64); err == nil && t >= 0 {
				timestamp = t
			}
		case "v1":
			if signature, err := hex.DecodeString(value); err == nil {
				signatures = append(signatures, signature)
			}
		}
	}
	if timestamp < 0 || len(signatures) == 0 {
		return false
	}
	if age := now.Sub(time.Unix(timestamp, 0)); age > tolerance || age < -tolerance {
		return false
	}
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(strconv.FormatInt(timestamp, 10) + "."))
	mac.Write(rawBody)
	expected := mac.Sum(nil)
	for _, signature := range signatures {
		if hmac.Equal(expected, signature) {
			return true
		}
	}
	return false
}

// body, _ := io.ReadAll(r.Body)
// ok := VerifySignature(r.Header.Get("X-LMS-Signature"), body, secret, 5*time.Minute, time.Now())

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

// Checks X-LMS-Signature: t={timestamp},v1={hex}[,v1={hex}] against the raw request body (a Buffer).
export function verifySignature(header, rawBody, secret, { tolerance = 300, now = Date.now() / 1000 } = {}) {
  let timestamp = null;
  const signatures = [];
  for (const part of header.split(",")) {
    const [key, value = ""] = part.trim().split("=", 2);
    if (key === "t" && /^\d+$/.test(value)) timestamp = Number(value);
    else if (key === "v1") signatures.push(value);
  }
  if (timestamp === null || signatures.length === 0) return false;
  if (Math.abs(now - timestamp) > tolerance) return false;
  const expected = createHmac("sha256", secret).update(`${timestamp}.`).update(rawBody).digest();
  return signatures.some((signature) => {
    const given = Buffer.from(signature, "hex");
    return given.length === expected.length && timingSafeEqual(given, expected);
  });
}

// Express: app.post("/hooks/training", express.raw({ type: "application/json" }), (req, res) => {
//   if (!verifySignature(req.get("X-LMS-Signature") ?? "", req.body, process.env.WEBHOOK_SECRET)) return res.sendStatus(401);
//   res.sendStatus(204); // then process the event asynchronously
// });

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

public static class WebhookSignature
{
    /// <summary>Checks X-LMS-Signature: t={timestamp},v1={hex}[,v1={hex}] against the raw request body.</summary>
    public static bool Verify(string header, byte[] rawBody, string secret, TimeSpan? tolerance = null, DateTimeOffset? now = null)
    {
        long? timestamp = null;
        var signatures = new List<string>();
        foreach (var part in header.Split(','))
        {
            var pair = part.Trim().Split('=', 2);
            if (pair.Length != 2) continue;
            if (pair[0] == "t" && long.TryParse(pair[1], out var t) && t >= 0) timestamp = t;
            else if (pair[0] == "v1") signatures.Add(pair[1]);
        }
        if (timestamp is null || signatures.Count == 0) return false;

        var age = (now ?? DateTimeOffset.UtcNow) - DateTimeOffset.FromUnixTimeSeconds(timestamp.Value);
        if (age.Duration() > (tolerance ?? TimeSpan.FromMinutes(5))) return false;

        var payload = Encoding.UTF8.GetBytes($"{timestamp}.").Concat(rawBody).ToArray();
        var expected = Encoding.ASCII.GetBytes(Convert.ToHexString(HMACSHA256.HashData(Encoding.UTF8.GetBytes(secret), payload)).ToLowerInvariant());
        return signatures.Any(s => CryptographicOperations.FixedTimeEquals(expected, Encoding.ASCII.GetBytes(s)));
    }
}

// ASP.NET Core: read the raw body before model binding, e.g.
// using var buffer = new MemoryStream(); await Request.Body.CopyToAsync(buffer);
// WebhookSignature.Verify(Request.Headers["X-LMS-Signature"].ToString(), buffer.ToArray(), secret);

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.HexFormat;
import java.util.List;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public final class WebhookSignature {
    private WebhookSignature() {
    }

    /** Checks X-LMS-Signature: t={timestamp},v1={hex}[,v1={hex}] against the raw request body. */
    public static boolean verify(String header, byte[] rawBody, String secret) throws Exception {
        return verify(header, rawBody, secret, 300, System.currentTimeMillis() / 1000);
    }

    public static boolean verify(String header, byte[] rawBody, String secret, long toleranceSeconds, long now) throws Exception {
        long timestamp = -1;
        List<String> signatures = new ArrayList<>();
        for (String part : header.split(",")) {
            String[] pair = part.trim().split("=", 2);
            if (pair.length != 2) {
                continue;
            }
            if (pair[0].equals("t") && pair[1].matches("\\d+")) {
                timestamp = Long.parseLong(pair[1]);
            } else if (pair[0].equals("v1")) {
                signatures.add(pair[1]);
            }
        }
        if (timestamp < 0 || signatures.isEmpty() || Math.abs(now - timestamp) > toleranceSeconds) {
            return false;
        }
        Mac mac = Mac.getInstance("HmacSHA256");
        mac.init(new SecretKeySpec(secret.getBytes(StandardCharsets.UTF_8), "HmacSHA256"));
        mac.update((timestamp + ".").getBytes(StandardCharsets.UTF_8));
        byte[] expected = HexFormat.of().formatHex(mac.doFinal(rawBody)).getBytes(StandardCharsets.US_ASCII);
        for (String signature : signatures) {
            if (MessageDigest.isEqual(expected, signature.getBytes(StandardCharsets.US_ASCII))) {
                return true;
            }
        }
        return false;
    }
}