/api routes and the authentication handled by the brilliant express-firebase-middleware

routes.js

...

router.use('/api', cors(), firebaseMiddleware.auth);
router.get('/api/hello', (req, res) => {
    res.json({
        message: `You're logged in as ${res.locals.user.email} with Firebase UID: ${res.locals.user.uid}`
    });
});

...