Signed webhooks

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

// rawBody: the body exactly as it arrived (string or Buffer), before
// JSON.parse. headers: the request's headers (Node lowercases the names).
export function verifySmpSignature(rawBody, headers, secret, options = {}) {
  const { toleranceSeconds = 300, now = Date.now() } = options;
  const signature = headers['x-smp-signature'];
  const timestamp = headers['x-smp-timestamp'];
  if (typeof signature !== 'string' || !/^\d+$/.test(timestamp ?? '')) {
    return false;
  }
  if (Math.abs(now / 1000 - Number(timestamp)) > toleranceSeconds) {
    return false;
  }
  const expected = createHmac('sha256', secret)
    .update(`${timestamp}.`)
    .update(rawBody)
    .digest();
  const given = Buffer.from(signature, 'hex');
  return given.length === expected.length && timingSafeEqual(given, expected);
}

<?php
// $rawBody: file_get_contents('php://input'), before any json_decode.
// $signature: $_SERVER['HTTP_X_SMP_SIGNATURE']
// $timestamp: $_SERVER['HTTP_X_SMP_TIMESTAMP']
function smp_verify_signature(
    string $rawBody,
    string $signature,
    string $timestamp,
    string $secret,
    int $toleranceSeconds = 300,
    ?int $now = null
): bool {
    if (!ctype_digit($timestamp)) {
        return false;
    }
    $now = $now ?? time();
    if (abs($now - (int) $timestamp) > $toleranceSeconds) {
        return false;
    }
    $expected = hash_hmac('sha256', $timestamp . '.' . $rawBody, $secret);
    return hash_equals($expected, strtolower($signature));
}

import hashlib
import hmac
import time
from typing import Optional


def verify_smp_signature(raw_body: bytes, signature: str, timestamp: str,
                         secret: str, tolerance_seconds: int = 300,
                         now: Optional[float] = None) -> bool:
    """raw_body: the body exactly as it arrived (Flask: request.get_data())."""
    if not (timestamp.isascii() and timestamp.isdigit()):
        return False
    current = time.time() if now is None else now
    if abs(current - int(timestamp)) > tolerance_seconds:
        return False
    message = timestamp.encode() + b"." + raw_body
    expected = hmac.new(secret.encode(), message, hashlib.sha256).hexdigest()
    return hmac.compare_digest(expected, signature.lower())