Verifying webhook signatures

signature = "sha256=" + hex(HMAC_SHA256(secret, `${timestamp}.${body}`))

X-Reader-Signature: sha256=abc123def456...
X-Reader-Timestamp: 1712275200

import express from "express";
import crypto from "crypto";

const app = express();

app.post(
  "/hooks/reader",
  express.raw({ type: "application/json" }),
  (req, res) => {
    const signature = req.headers["x-reader-signature"] as string;
    const timestamp = req.headers["x-reader-timestamp"] as string;
    const body = req.body as Buffer; // raw bytes

    // 1. Replay protection: reject timestamps older than 5 minutes
    const age = Math.floor(Date.now() / 1000) - parseInt(timestamp, 10);
    if (Number.isNaN(age) || age > 300) {
      return res.status(400).send("stale");
    }

    // 2. Recompute the signature
    const expected =
      "sha256=" +
      crypto
        .createHmac("sha256", process.env.READER_WEBHOOK_SECRET!)
        .update(`${timestamp}.${body.toString("utf8")}`)
        .digest("hex");

    // 3. Constant-time compare
    const a = Buffer.from(signature);
    const b = Buffer.from(expected);
    if (a.length !== b.length || !crypto.timingSafeEqual(a, b)) {
      return res.status(401).send("invalid signature");
    }

    // Good: parse the body now
    const payload = JSON.parse(body.toString("utf8"));
    handleEvent(req.headers["x-reader-event"] as string, payload);

    res.status(200).end();
  },
);

import hmac
import hashlib
import os
import time

from fastapi import FastAPI, Request, HTTPException

app = FastAPI()
SECRET = os.environ["READER_WEBHOOK_SECRET"].encode()


@app.post("/hooks/reader")
async def reader_webhook(request: Request):
    body = await request.body()  # raw bytes
    signature = request.headers.get("x-reader-signature", "")
    timestamp = request.headers.get("x-reader-timestamp", "")

    # 1. Replay protection
    try:
        age = int(time.time()) - int(timestamp)
    except ValueError:
        raise HTTPException(400, "bad timestamp")
    if age > 300:
        raise HTTPException(400, "stale timestamp")

    # 2. Recompute
    expected = (
        "sha256="
        + hmac.new(SECRET, f"{timestamp}.{body.decode()}".encode(), hashlib.sha256).hexdigest()
    )

    # 3. Constant-time compare
    if not hmac.compare_digest(signature, expected):
        raise HTTPException(401, "invalid signature")

    import json
    payload = json.loads(body)
    handle_event(request.headers["x-reader-event"], payload)
    return {"ok": True}

// app/api/hooks/reader/route.ts
import crypto from "crypto";
import { NextRequest, NextResponse } from "next/server";

export async function POST(req: NextRequest) {
  const body = await req.text(); // raw body as a string
  const signature = req.headers.get("x-reader-signature") ?? "";
  const timestamp = req.headers.get("x-reader-timestamp") ?? "";

  const age = Math.floor(Date.now() / 1000) - parseInt(timestamp, 10);
  if (Number.isNaN(age) || age > 300) {
    return new NextResponse("stale", { status: 400 });
  }

  const expected =
    "sha256=" +
    crypto
      .createHmac("sha256", process.env.READER_WEBHOOK_SECRET!)
      .update(`${timestamp}.${body}`)
      .digest("hex");

  const a = Buffer.from(signature);
  const b = Buffer.from(expected);
  if (a.length !== b.length || !crypto.timingSafeEqual(a, b)) {
    return new NextResponse("invalid signature", { status: 401 });
  }

  const payload = JSON.parse(body);
  // ... handle event ...

  return NextResponse.json({ ok: true });
}