How to use the follow-redirects.https.Agent function in follow-redirects

/*! @license MIT ©2016 Ruben Verborgh, Ghent University - imec */
/* Single-function HTTP(S) request module */

var EventEmitter = require('events').EventEmitter,
    _ = require('lodash'),
    url = require('url'),
    http = require('follow-redirects').http,
    https = require('follow-redirects').https,
    zlib = require('zlib');

// Try to keep connections open, and set a maximum number of connections per server
var AGENT_SETTINGS = { keepAlive: true, maxSockets: 5 };
var AGENTS = {
  http:  new http.Agent(AGENT_SETTINGS),
  https: new https.Agent(AGENT_SETTINGS),
};

// Decode encoded streams with these decoders
var DECODERS = { gzip: zlib.createGunzip, deflate: zlib.createInflate };

// Creates an HTTP request with the given settings
function createRequest(settings) {
  // Parse the request URL
  if (settings.url)
    _.assign(settings, url.parse(settings.url));

  // Emit the response through a proxy
  var request, requestProxy = new EventEmitter(),
      requester = settings.protocol === 'http:' ? http : https;
  settings.agents = AGENTS;
  request = requester.request(settings, function (response) {

'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8',
        'Accept-Encoding': 'gzip,deflate,sdch',
        'Accept-Language': 'en-US,en;q=0.8',
        'Cache-Control': 'no-cache',
        'Connection': 'keep-alive',
        'User-Agent': 'cleverstack'
      },
      rejectUnauthorized: false,
      secureProtocol: require('constants').SSL_OP_NO_TLSv1_2
    };

  var proxy = process.env.HTTPS_PROXY || process.env.HTTP_PROXY || null;
  if (proxy !== null) {
    options.agent = new proxyAgent(proxy);
  } else {
    options.agent = new https.Agent(options);
  }

  return download(options, dir);
};