AuthController.js

var Auth = require('../services/AuthService')

module.exports = {
    login: function(req, res) {
        Auth.login(req.body, function(err) {
            if (err) return res.status(401).json({
                message: 'You are not authorized'
            })

            res.status(200).json({
                message: 'You are authorized'
            })
        })
    },
    signup: function(req, res) {
        Auth.signup(req.body, function(err, newUser) {
            if (err) return res.status(400).json({
                message: 'No email provided...'
            })

            Auth.login(newUser, function(err) {
                // so on so forth...
                if (err) return res.status(400).json({
                    message: '...'
                })
                res.status(201).json(newUser)
            })
        })
    }
}

AuthService.js

var mongoskin = require('mongoskin');

module.exports = {
    login: function(credentials, callback) {
        req.db.collection('auth').findOne({
                _id: mongoskin.helper.toObjectID(credentials.id)
            },
            function(err, results) {
                if (err) return callback(err)

                // Return null if successful
                return callback(null)
                    // log person in and send results to client
            }
        )
    },
    signup: function(userDetails, callback) {
        req.db.collection('auth').insert(userDetails, function(err, newUser) {
            if (err) return callback(err);

            return callback(null, newUser)

        })
    }
}