Webhooks

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

export function verify(rawBody: string, header: string, secret: string): boolean {
  const parts = Object.fromEntries(
    header.split(",").map((kv) => kv.split("=", 2)),
  ) as { t?: string };
  const t = parts.t;
  if (!t) return false;

  // Reject anything older than five minutes: the timestamp is inside the
  // signed string, so a captured delivery cannot be replayed with a fresh t,
  // but it CAN be replayed verbatim until you decide it is too old.
  if (Math.abs(Date.now() / 1000 - Number(t)) > 300) return false;

  const expected = createHmac("sha256", secret).update(`${t}.${rawBody}`).digest();

  // A rotation sends TWO v1= values — the second signed with the previous
  // secret. Accept either, or an in-flight retry fails the moment you rotate.
  return header
    .split(",")
    .filter((kv) => kv.startsWith("v1="))
    .some((kv) => {
      const sig = Buffer.from(kv.slice(3), "hex");
      return sig.length === expected.length && timingSafeEqual(sig, expected);
    });
}

import hmac, hashlib, time

def verify(raw_body: bytes, header: str, secret: str) -> bool:
    parts = dict(p.split("=", 1) for p in header.split(","))
    t = parts.get("t")
    if not t or abs(time.time() - int(t)) > 300:
        return False

    expected = hmac.new(
        secret.encode(), f"{t}.".encode() + raw_body, hashlib.sha256
    ).hexdigest()

    # Two v1= values during a rotation overlap; either may match.
    return any(
        hmac.compare_digest(p[3:], expected)
        for p in header.split(",")
        if p.startswith("v1=")
    )