Issue with Google oAuth2 callback using Firebase functions - node.js

Question

I would like use Firebase Functions to use the Google Developer API. Authentification is required to use this API.
I follow the doc: https://github.com/googleapis/google-api-nodejs-client
I have some troubles to get the authorization code in the callback url.
var {google} = require('googleapis');
google.options({ auth: oauth2Client });
var oauth2Client = new google.auth.OAuth2(
'XXXX.apps.googleusercontent.com',
'XXXX',
'https://us-central1-XXXX.cloudfunctions.net/oauth2callback'
);
function generateAuthenticationUrl() {
return oauth2Client.generateAuthUrl({
access_type: 'offline',
prompt: 'consent',
scope: 'https://www.googleapis.com/auth/androidpublisher'
});
}
exports.oauth2Callback = functions.https.onRequest((req, res) => {
console.log(req.query.code);
const code = req.query.code;
//do something
return null;
});
exports.hello = functions.https.onRequest((req, res) => {
var url = generateAuthenticationUrl();
console.log(url);
//-> url print in the console is : https://accounts.google.com/o/oauth2/v2/auth?access_type=offline&prompt=consent&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fandroidpublisher&response_type=code&client_id=XXXXX-XXX.apps.googleusercontent.com&redirect_uri=https%3A%2F%2Fus-central1-XXX.cloudfunctions.net%2Foauth2callback
res.redirect(url);
});
Redirect url is set in the Google Console Developer:
When I call the url https://us-central1-XXX.cloudfunctions.net/hello, I got "Error: could not handle the request" and "finished with status: 'timeout'" in the Firebase logs.
What's wrong?

Answer 1

I found a solution.
Full code using JWT to authenticate, then get the list of app's reviews:
const functions = require('firebase-functions')
const admin = require('firebase-admin')
admin.initializeApp(functions.config().firebase);
var {google} = require('googleapis');
const serviceAccount = require('./client_secret.json');
const { JWT } = require('google-auth-library');
const getAuthorizedClient = () => new JWT({
email: serviceAccount.client_email,
key: serviceAccount.private_key,
scopes: ['https://www.googleapis.com/auth/androidpublisher']
});
const getAndroidpublisher = () => google.androidpublisher({
version: 'v3',
auth: getAuthorizedClient()
});
const requestProductValidation = () => new Promise((resolve, reject) => {
getAndroidpublisher().reviews.list({
packageName: "com.my.packagename"
}, (err, response) => {
if (err) {
console.log(`The API returned an error: ${err}`);
resolve({status: "Error"});
} else {
return resolve(response);
}
});
});
exports.hello = functions.https.onRequest((req, res) => {
return requestProductValidation();
});