adLogin.js

let adConfig = {
  url:'',
  baseDN: '',
  username: '',
  password: ''
}

const ActiveDirectory = require('activedirectory2').promiseWrapper
      , ad = new ActiveDirectory(adConfig)

module.exports = (params, callback) => {
   ad.authenticate(params.username, params.password).then((auth) => {
      if(auth) {
        // establish a session using express-session
        // return true
      }
   }
}

app.js

const express = require('express')
      , app = express()

let isLogin = require('./controllers/isLogin.js')

app.use('/', isLogin, require('./routes/secureRoutes.js')());

isLogin.js

const adCheck = require('./adLogin')

module.exports = (req,res,next) => {
  adCheck(req.body, (auth) => {
    if(auth === true) next()
  })
}

secureRoutes.js

const express = require('express')
      , secureRouter = express.Router()

module.exports = () => {
  secureRouter.get('/foo', (req, res) => {
    res.json({
      foo:'bar'
    })
  });

  secureRouter.get('/foo2', (req, res) => {
    res.json({
      foo2:'bar2' 
    })
  });

  return secureRouter;
}