github-webhook-validator

This library provides an Express middleware validator for GitHub webhooks that have a secret key defined.

It was primarily developed for the pages-server. It enables authentication across multiple webhooks handled by the same server.

Installation

To make this library part of your project:

$ npm install github-webhook-validator --save

Note that Node.js version 4.8.5 or higher is required; check your installed version with node -v.

Usage

During the initialization phase of your application:

var express = require('express');
var bodyParser = require('body-parser');
var webhookValidator = require('github-webhook-validator');
 
module.exports.launchServer = function(config) {
  // loadKeyDictionary returns a Promise that creates an object comprised of
  // `label: key` mappings.
  return webhookValidator.loadKeyDictionary(
    config.secretKeyFile, config.builders)
    .then(function(keyDictionary) { return doLaunch(config, keyDictionary); })
    .catch(function(err) { console.error('Failed to start server:', err); });
}
 
function doLaunch(config, keyDictionary) {
  // Once the keyDictionary is loaded, create a middlewareValidator that can
  // be passed to Express middleware body parsers.
  var middlewareOptions = {
    verify: webhookValidator.middlewareValidator(keyDictionary)
  };
  var server = express();
  server.use(bodyParser.json(middlewareOptions));
 
  // Continue server initialization...
}

API

loadKeyDictionary([defaultKeyFile[, builderConfigs[, parseKeyLabelFromConfig]]])

Returns a Promise that will, upon success, resolve to an object comprised of label: key mappings for use by the middleware validator.

• defaultKeyFile: path to the file containing the secret key used to validate all payloads by default
• builderConfigs: array of objects pertaining to individual branches or other entities managed by the webhook server
  • Each may contain an optional secretKeyFile member, which will be used in place of the top-level defaultKeyFile for that builder.
• parseKeyLabelFromConfig: maps each element of builderConfigs to a label for the element's secretKeyFile contents
  • The default parser returns the value of the element's branch member, as the original use case supports differentiating webhooks by branch.

It is possible for defaultKeyFile to be undefined, while individual builderConfigs have their own secretKeyFile definitions.

If no arguments are defined, the Promise will resolve to an empty object, effectively disabling validation, except that any incoming webhooks with the X-Hub-Signature HTTP header defined will fail validation. The solution would be to add the secret key to the server, or to remove it from the webhook definition.

middlewareValidator(keyDictionary[, parseKeyLabelFromBody])

Returns a function corresponding to the verify function interface passed as an option to Express body-parser middleware. The returned function will abort the request with an error message if validation fails, prior to parsing taking place.

• keyDictionary: the result from loadKeyDictionary()
• parseKeyLabelFromBody: maps the raw contents of the request body to a label for one of the keys within keyDictionary
  • The default parser parses the name of the branch from the ref field, if present.

Raises:

• ValidationError: if validation fails for any reason; this object contains:
  • keyLabel: the value returned from parseKeyLabelFromBody
  • webhookId: the value of the X-GitHub-Delivery HTTP header
  • ip: the IP address of the request source

If the parser returns null or undefined, or if the value does not match a member of keyDictionary, the value of the defaultKeyFile from loadKeyDictionary() will be used as the secret key, if it exists. If it does not exist, any incoming requests with the X-Hub-Signature HTTP header will fail validation. The fix would be to add a default key, to add a branch-specific key, or to remove the secret key from the webhook definition.

Open Source License

This software is made available as Open Source software under the ISC License. For the text of the license, see the LICENSE file.