Webhooks & signatures

import crypto from 'node:crypto';

// Mount with express.raw({ type: 'application/json' }): the signature covers the
// exact bytes we sent, so re-serialising a parsed body will not match.
export function verify(rawBody, headers, secrets) {
  const timestamp = Number(headers['x-qannasapi-timestamp']);
  if (!Number.isFinite(timestamp)) return false;
  if (Math.abs(Date.now() / 1000 - timestamp) > 300) return false; // replay window

  const presented = String(headers['x-qannasapi-signature'])
    .split(',')
    .map((part) => part.trim().split('=')[1])
    .filter(Boolean);

  // Accept a match against ANY held secret — that is what makes rotation
  // seamless while both the old and new secret are in play.
  return secrets.some((secret) => {
    const expected = crypto
      .createHmac('sha256', secret)
      .update(`${timestamp}.`)
      .update(rawBody)
      .digest('hex');
    return presented.some(
      (digest) =>
        digest.length === expected.length &&
        crypto.timingSafeEqual(Buffer.from(digest), Buffer.from(expected)),
    );
  });
}

import hashlib
import hmac
import time

def verify(raw_body: bytes, headers: dict, secrets: list[str]) -> bool:
    try:
        timestamp = int(headers["x-qannasapi-timestamp"])
    except (KeyError, ValueError):
        return False
    if abs(time.time() - timestamp) > 300:  # replay window
        return False

    presented = [
        part.strip().split("=", 1)[1]
        for part in headers.get("x-qannasapi-signature", "").split(",")
        if "=" in part
    ]
    signed = str(timestamp).encode() + b"." + raw_body

    # Accept a match against ANY held secret (rotation overlap).
    for secret in secrets:
        expected = hmac.new(secret.encode(), signed, hashlib.sha256).hexdigest()
        if any(hmac.compare_digest(digest, expected) for digest in presented):
            return True
    return False