Fetch all the groups a user is member of with ldapjs

setup_passport.js

var Users = require('./Users');
var users = new Users();

passport.use(new WindowsStrategy({ 
  ldap: {
    url:             process.env["LDAP_URL"],
    base:            process.env["LDAP_BASE"],
    bindDN:          process.env["LDAP_BIND_USER"],
    bindCredentials: process.env["LDAP_BIND_PASSWORD"]
  },
  integrated: false
}, function(profile, done){
  if (!profile) return done(null, false);
  users.getAllGroups(profile._json, function (err, groups) {
    if (err) return done (err);
    profile.groups = groups.map(function (g) {
      return g.cn;
    });
    done(null, profile);
  });
}));

Users.js

var nconf = require('nconf');
var ldap  = require('ldapjs');
var async = require('async');
ldap.Attribute.settings.guid_format = ldap.GUID_FORMAT_D;

var Users = module.exports = function(){
  var options = this._options = {
    url:             process.env["LDAP_URL"],
    base:            process.env["LDAP_BASE"],
    bindDN:          process.env["LDAP_BIND_USER"],
    bindCredentials: process.env["LDAP_BIND_PASSWORD"]
  };

  this._client = ldap.createClient({
    url:            options.url,
    maxConnections: 10,
    bindDN:         options.bindDN,
    credentials:    options.bindCredentials  
  });


  this._client.on('error', function(e){
    console.log('LDAP connection error:', e);
  });

  this._queue = [];

  var self = this;
  this._client.bind(options.bindDN, options.bindCredentials, function(err) {
    if(err){
        return console.log("Error binding to LDAP", 'dn: ' + err.dn + '\n code: ' + err.code + '\n message: ' + err.message);
    }
    self.clientConnected = true;
    self._queue.forEach(function (cb) { cb(); });
  });
};

Users.prototype.getAllGroups = function (obj, callback) {
  var self = this;
  self.getGroups(obj, function (err, groups) {
    if (err) return callback(err);
    
    async.map(groups, self.getAllGroups.bind(self), function (err, res) {
      return callback(err, groups.concat.apply(groups, res));
    });
  });
};

Users.prototype.getGroups = function (obj, callback) {
  var self = this;
  
  var opts = { 
    scope: 'sub',
    filter: '(&(objectclass=group)(member=' + obj.dn + '))' 
  };
  
  self._client.search(self._options.base, opts, function(err, res){
    if (err) {
      console.log('List groups error:', err);
      return callback(err);
    }
    var entries = [];
    res.on('searchEntry', function(entry) {
      entries.push(entry);
    });

    function done () {
      if(entries.length === 0) return callback(null, []);
      var result = entries.map(function (e) { return e.object; });
      callback(null, result);
    }

    res.on('error', function(err) {
      if (err.message === 'Size Limit Exceeded') return done(); 
      callback(err);
    });
    
    res.on('end', done);
  });
};

As someone who's a novice at JS and has never used ldapjs before, this is really hard to understand. Can you comment or explain this please?
Titled, this should in theory do exactly what I'm after, but damn if I can work out how to implement it.

where do you declare "passport" variable?