Validating Kentico Cloud webhooks signatures in Express.js

How to validate webbooks signature using express.js?

In docs, there is a section about notification signatures but I don't know how to combine it with Express.js

This question is a migrated from official Kentico Cloud Forum, that would be deleted.

In the API reference, there is a sample describing webhook validation in various languages including node.js.

If you want to use express.js you could start with this template code:

const express = require('express');
const crypto = require('crypto');

// Create a new instance of express
const app = express();

// Set up a raw bodyparser to read the webhook post
const bodyParserRaw = require('body-parser').raw({
    type: '*/*',
});

function webhookValidator (req, res, next) {
    // get the header signature from the webhook request
    const givenSignature = req.headers['x-kc-signature'];

    // throw error if it's missing
    if (!givenSignature) {
        console.log('Missing signature');
        return res.status(409).json({
            error: 'Missing signature'
        });
    }

    // create HMAC from the raw request body
    let hmac = crypto.createHmac('sha256', [your-webhook-secret-key]);
    hmac.write(req.body);
    hmac.end();

    // get a base64 hash from HMAC
    let hash = hmac.read().toString('base64');

    // check validity with timingSafeEqual
    let webhookValid = false;
    try {
        webhookValid = crypto.timingSafeEqual(Buffer.from(givenSignature, 'base64'), Buffer.from(hash, 'base64'));
    } catch (e) {
        webhookValid = false
    }

    // return validity
    if (webhookValid) {
        return next();
    } else {
        console.log('Invalid signature');
        return res.status(409).json({
            error: 'Invalid signature'
        });
    }
}

// create a route and pass through the bodyparser and validator
app.post('/webhook', bodyParserRaw, webhookValidator, ( req, res, next ) => {
    // If execution gets here, the HMAC is valid
    console.log('webhook is valid');
});

EDIT

You can use the Kontent webhook helper library to quickly verify the webhook notifications and their signatures. The library is available as @kentico/kontent-webhook-helper npm package and helps you avoid common problems when calculating the hash.