login.js

var Flow = require('make-flow')
var crypto = require('crypto')

function Hash (str) {
  var salt = '%9023t89gisuhslKLJifsdjl;apasfk<klas,Q%G@0jq39'
  return crypto.createHash('sha256').update(salt + str).digest('hex')
}

var login = Flow()
.def('users', function (done) {
  db.collection('user', done)
})
.def('username', function (req) {
  if (!req.username) throw new Error('Username is not passed')
  return req.username
})
.def('password', function (req) {
  if (!req.password) throw new Error('Password is not passed')
  return req.password
})
.def('exists', function (users, username, password, done) {
  users.findOne({username: username, password: Hash(password)}, function (err, usr) {
    done(err, !!user)
  })
})
.def('login', function (username, exists, users, done) {
  if (!exists) return done(new Error('User not found'))
  var token = Hash(Math.random())
  users.update({username: username}, {$set: {authToken: token}}, function (err) {
    done(err, token)
  })
})

module.exports = function (req, res, next) {
  login.run().set('req', req).eval('login', function (err, login) {
    if (!err) return res.send({authToken: login})
    if (err._task == 'username' || err._task == 'password' || /not found/.test(err.message)) {
      err.status = 406
    } else {
      err.status = 500
    }
    next(err)
  })
}