PHPでgetallheaders()が動かない時用の関数 https://stackoverflow.com/questions/13224615/get-the-http-headers-from-current-request-in-php

getallheaders.php

<?php
  if (!function_exists('getallheaders')) {
    function getallheaders() {
      $headers = array();

      foreach ($_SERVER as $name => $value) {
        if (substr($name, 0, 5) == 'HTTP_') {
          $headers[str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5)))))] = $value;
        }
      }

      return $headers;
    }
  }
  
  // ヘッダー情報を出力
  print_r(getallheaders());
?>