.js

var expressPromiseRouter = require("express-promise-router");
var router = expressPromiseRouter();
var Promise = require("bluebird");
function authenticate(email, password) {
    return Promise.try(function() {
        return knex('users').where('email', email);
    }).then(function(rows) {
        if (rows.length === 0) {
            throw new Error('cannot find user');
        }
        
        var user = rows[0];
        
        return Promise.try(function() {
            return scrypt.verifyHash(password, user.password);
        }).then(function(valid) {
            // valid is always true, if we get to this point.
            return user;
        });
    });
}
router.post('/login', function (req, res) {
    return Promise.try(function() {
        return authenticate(req.body.email, req.body.password);
    })
    .then(function(user) {
        // Regenerate session when signing in
        // to prevent fixation
        req.session.regenerate(function () {
            // Store the user's primary key
            // in the session store to be retrieved,
            // or in this case the entire user object
            req.session.user = user;
            req.session.success = 'Login successful!';
            res.redirect('/cards');
        });
    })
    .catch(scrypt.PasswordError, function(error) {
        req.session.error = 'Authentication failed, please check your username and password.';
        res.redirect('/login');
    });
});