Error using the GitHub Webhook example

Situation

I am setting up the aws-node-github-webhook-listener example for a project at Netlify and running into the error where the generated sha1 create from my secret GitHub token set in my webhook settings never matched the one in header['X-Hub-Signature'].

Complication

There is a function that creates sha1 based on the github event body and secret key.

function signRequestBody(key, body) {
  // key is my secret
  return `sha1=${crypto.createHmac('sha1', key).update(body, 'utf-8').digest('hex')}`;
}

Question

TBH, I don't have ever encountered a problem where I needed to compared encrypted data. Is there that someone has a working example of this in the wild? Is there is something I am overlooking?

My function works fine of course if I remove this secret checking, but my guess is @DavidWells has this working as is 😄. Just need some gentle nudging in the correct direction.

Error Message

Error Message from my logs:

{"errorMessage":"[401] X-Hub-Signature incorrect. Github webhook token doesn't match","errorType":"Error","stackTrace":["module.exports.githubWebhookListener (/var/task/handler.js:52:21)"]}

// serverless.yml

service: netlify-cms-www-webhook

provider:
  name: aws
  runtime: nodejs6.10
  environment:
    GITHUB_WEBHOOK_SECRET: unencrytedSecret
    NETLIFY_WEBHOOK_BUILD: https://api.netlify.com/build_hooks/12345

Live Code is at https://github.com/netlify/netlify-cms-docs-webhook

The relevant entry point is aws-node-github-webhook-listener/handler.js, especially the linked signature check around lines 36–39; also inspect the serverless.yml secret configuration. Reproduce the webhook request and compare the generated signature with X-Hub-Signature, then verify that valid requests are accepted and invalid ones are rejected.