How to setup an authentication middleware in Express.js

You can create a new module called auth.js and then use it to check if users are authorized or not:

auth.js

module.exports.isAuthorized  = function(req, res, next) {

    User.findById(req.session.userId).exec(function (error, user) {
        if (error) {
            return next(error);
        } else {      
            if (user === null) {     
                var err = new Error('Not authorized! Go back!');
                err.status = 401;
                return next(err);
            } else {
                return next();
            }
        }
    });
}

routes.js

var auth = require('./auth');

// GET route after registering
router.get('/clientPage', auth.isAuthorized, function (req, res, next) {
    res.sendFile(path.join(__dirname + '/../views/clientPage.html'));
});

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