Stripe Error: No signatures found matching the expected signature for payload

I have a stripe webhook that call a Firebase function. In this function I need to verify that this request comes from Stripe servers. Here is the code :

const functions = require('firebase-functions');
const bodyParser = require('body-parser');
const stripe = require("stripe")("sk_test_****");
const endpointSecret = 'whsec_****';
const app = require('express')();

app.use(bodyParser.json({
    verify: function (req, res, buf) {
        var url = req.originalUrl;
        if (url.startsWith('/webhook')) {
            req.rawBody = buf.toString()
        }
    }
}));

app.post('/webhook/example', (req, res) => {
    let sig = req.headers["stripe-signature"];

    try {
        console.log(req.bodyRaw)
        let event = stripe.webhooks.constructEvent(req.body, sig, endpointSecret);
        console.log(event);
        res.status(200).end()

        // Do something with event
    }
    catch (err) {
        console.log(err);
        res.status(400).end()
    }
});

exports.app = functions.https.onRequest(app);

As mentioned in Stripe Documentation, I have to use raw body to perform this security check.

I have tried with my current code and with :

app.use(require('body-parser').raw({type: '*/*'}));

But I always get this error :

Error: No signatures found matching the expected signature for payload. Are you passing the raw request body you received from Stripe? https://github.com/stripe/stripe-node#webhook-signing

Cloud Functions automatically parses body content of known types. If you're getting JSON, then it's already parsed and available to you in req.body. You shouldn't need to add other body parsing middleware.

If you need to process the raw data, you should use req.rawBody, but I don't think you'll need to do that here.