How to Add Expire Headers for External Scripts

We’re going to add Expire header on this

<script type="text/javascript" src="https://ssl.google-analytics.com/ga.js"></script>

Create a .php file externaljs.php

<?php
 $files = array(
 'ga.js' => 'https://ssl.google-analytics.com/ga.js',
 'bsa.js' => 'https://s3.buysellads.com/ac/bsa.js',
 'pro.js' => 'https://s3.buysellads.com/ac/pro.js'
);
 if(isset($files[$_GET['file']])) {
 if ($files[$_GET['file']] == 'ga.js'){
  header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + ((60 * 60) * 48))); // 2 days for GA
 } else {
  header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + (60 * 60))); // Default set to 1 hour
 }
  echo file_get_contents($files[$_GET['file']]);
}
 ?>

After that replace analytics script with this

<script type="text/javascript" src="externaljs.php?url=ga.js"></script>