pnp4nagios authenticate with Icinga

usr_local_pnp4nagios_share_index.php

<?php

namespace Icinga;
class User extends \stdClass {
  public $localUsername;
  public $groups;
}

function icinga_login() {
    header("Location: /authentication/login");
    die();
}

if (isset($_COOKIE['Icingaweb2'])) {
    $sessionfile = ini_get("session.save_path")."/sess_".$_COOKIE['Icingaweb2'];
    if (file_exists($sessionfile)) {
        $sessiondata = file_get_contents($sessionfile);
        session_start();
        session_decode($sessiondata);
        if (empty($_SESSION['user'])) {
            icinga_login();
        }
        if (!in_array("Administrators", $_SESSION['user']->groups)) {
            error_log("user (". $_SESSION['user']->localUsername .") has icinga cookie but is not in Administrators group");
            die();
        }
        session_destroy();
    }else {
        // session does not exist on disk. timeout.
        icinga_login();
    }
}else {
    // no Icingaweb2 cookie passed.
    icinga_login();
}

// Rest of original file remains untouched.