Verify GitHub webhook signature header in Node.js

githook.js

/*
 * Verify GitHub webhook signature header in Node.js
 * Written by stigok and others (see gist link for contributor comments)
 * https://gist.github.com/stigok/57d075c1cf2a609cb758898c0b202428
 * Licensed CC0 1.0 Universal
 */

const crypto = require('crypto')
const express = require('express')
const bodyParser = require('body-parser')

const secret = CHANGE_ME;

// For these headers, a sigHashAlg of sha1 must be used instead of sha256
// GitHub: X-Hub-Signature
// Gogs:   X-Gogs-Signature
const sigHeaderName = 'X-Hub-Signature-256'
const sigHashAlg = 'sha256'

const app = express()

// Saves a valid raw JSON body to req.rawBody
// Credits to https://stackoverflow.com/a/35651853/90674
app.use(bodyParser.json({
  verify: (req, res, buf, encoding) => {
    if (buf && buf.length) {
      req.rawBody = buf.toString(encoding || 'utf8');
    }
  },
}))

function verifyPostData(req, res, next) {
  if (!req.rawBody) {
    return next('Request body empty')
  }

  const sig = Buffer.from(req.get(sigHeaderName) || '', 'utf8')
  const hmac = crypto.createHmac(sigHashAlg, secret)
  const digest = Buffer.from(sigHashAlg + '=' + hmac.update(req.rawBody).digest('hex'), 'utf8')
  if (sig.length !== digest.length || !crypto.timingSafeEqual(digest, sig)) {
    return next(`Request body digest (${digest}) did not match ${sigHeaderName} (${sig})`)
  }

  return next()
}

app.post('/', verifyPostData, function (req, res) {
  res.status(200).send('Request body was signed')
})

app.use((err, req, res, next) => {
  if (err) console.error(err)
  res.status(403).send('Request body was not signed or verification failed')
})

app.listen(3000, () => console.log("Listening on port 3000"))

Thanks a lot !!!!

Does the request body get sent as a base64 encoded string? I'm trying to write an AWS lambda function to deal with this. Not sure if this is something that happens with AWS in general or if the payload actually gets sent as a base64 encoded string.

Does the request body get sent as a base64 encoded string? I'm trying to write an AWS lambda function to deal with this. Not sure if this is something that happens with AWS in general or if the payload actually gets sent as a base64 encoded string.

I recommend you read the API documentation for AWS lambda to find an answer to this. This code works as-is for incoming HTTP GitHub webhook requests.

I'm trying to figure this out while using Cloudflare Workers (and itty-router instead of express), anyone have any suggestions?