Implementing rest authentication in ember UI with express backend

I am pretty new to nodejs. What i need to know is what is the right way to implement authentication in ember UI and express rest api. Express api runs on a subdomain for the application. Here is the code that i have for authentication

router
    .post('/', function(req, res) {
        response = {}
        if (req.body.username == "") {
            response.status = "error";
            response.message = "Username field cannot be empty";
            res.statusCode = 400;
            return res.json(response);
        };
        if (req.body.password == "") {
            response.status = "error";
            response.message = "Password field cannot be empty";
            res.statusCode = 400;
            return res.json(response);
        };
        const db = req.db;
        const users = db.get('users');
        users.find({
            username: req.body.username
        }, {}, function(e, docs) {
            if (docs.length != 0) {
                response.status = "error";
                response.message = "Same username already exists";
                res.statusCode = 409;
                res.json(response);
            } else {
                bcrypt.hash(req.body.password, 5, function(err, bcryptedPassword) {
                    users.insert({
                        username: req.body.username,
                        password: bcryptedPassword,
                        admin: false
                    });
                    res.statusCode = 200;
                    res.send();
                });
            }

        });
    })
    .post('/authenticate', function(req, res) {
        response = {}
        if (req.body.username == "") {
            response.status = "error";
            response.message = "Username field cannot be empty";
            res.statusCode = 400;
            return res.json(response);
        };
        if (req.body.password == "") {
            response.status = "error";
            response.message = "Password field cannot be empty";
            res.statusCode = 400;
            return res.json(response);
        };
        const db = req.db;
        const users = db.get('users');
        users.find({
            username: req.body.username
        }, {}, function(e, docs) {
            if (docs.length == 1) {
                bcrypt.compare(req.body.password, docs[0].password, function(err, doesMatch) {
                    if (doesMatch) {
                        response.status = "success";
                        res.statusCode = 200;
                        var token = jwt.sign(docs[0], "test key", {
                            // expiresInMinutes: 1440 // expires in 24 hours
                        });
                        response.token = token;
                        res.json(response);
                    } else {
                        response.status = "error";
                        response.message = "Please check your username and password";
                        res.statusCode = 401;
                        res.json(response);
                    }
                });
            } else {
                response.status = "error";
                response.message = "Username not found";
                res.statusCode = 404;
                res.json(response);
            }

        });
    });

Now the question is in two parts. First how can i implement a middleware kind of thing that will open authentication modal wherever the user needs to be signed up.

Secondly i am pretty sure that i am going wrong on the express side of server and if anyone can point me to a node module that provides restfull authentication, that would be much appreciated.