<?php
//auth.php source code
error_reporting(0);
$realm = 'Private Area';
$users = array('admin' => 'cowboy123');

if (empty($_SERVER['PHP_AUTH_DIGEST'])) {
    header('HTTP/1.1 401 Unauthorized');
    header('WWW-Authenticate: Digest realm="'.$realm.'",qop="auth",nonce="'.time().'",opaque="'.md5($realm).'"');
    die('Access Denied');
}

if (!($data = http_digest_parse($_SERVER['PHP_AUTH_DIGEST'])) || !isset($users[$data['username']]))
    die('Access Denied');

$A1 = md5($data['username'] . ':' . $realm . ':' . $users[$data['username']]);
$A2 = md5($_SERVER['REQUEST_METHOD'].':'.$data['uri']);
$valid_response = md5($A1.':'.$data['nonce'].':'.$data['nc'].':'.$data['cnonce'].':'.$data['qop'].':'.$A2);

if (time() - $data['nonce'] > 600 || $data['response'] != $valid_response)
    die('Access Denied');

echo 'CTF{6ee8014f5cc43767d03d97d6d73d9ed5}';
//echo 'CTF{OLD_FLAG_OLD_FLAG_OLD_FLAG}';

function http_digest_parse($txt)
{
    $needed_parts = array('nonce'=>1, 'nc'=>1, 'cnonce'=>1, 'qop'=>1, 'username'=>1, 'uri'=>1, 'response'=>1);
    $data = array();
    $keys = implode('|', array_keys($needed_parts));

    preg_match_all('@(' . $keys . ')=(?:([\'"])([^\2]+?)\2|([^\s,]+))@', $txt, $matches, PREG_SET_ORDER);

    foreach ($matches as $m) {
        $data[$m[1]] = $m[3] ? $m[3] : $m[4];
        unset($needed_parts[$m[1]]);
    }

    return $needed_parts ? false : $data;
}
?>