Description:
------------
http://docs.php.net/manual/zh/features.http-auth.php

This page have the error!
"Example #7 Digest HTTP" 

Reproduce code:
---------------
<?php
$realm = 'Restricted area';

//user => password
$users = array('admin' => 'mypass', 'guest' => 'guest');


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

    die('Text to send if user hits Cancel button');
}


// analyze the PHP_AUTH_DIGEST variable
if (!($data = http_digest_parse($_SERVER['PHP_AUTH_DIGEST'])) ||
    !isset($users[$data['username']]))
    die('Wrong Credentials!');


// generate the valid response
$A1 = md5($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 ($data['response'] != $valid_response)
    die('Wrong Credentials!');

// ok, valid username & password
echo 'Your are logged in as: ' . $data['username'];


// function to parse the http auth header
function http_digest_parse($txt)
{
    // protect against missing data
    $needed_parts = array('nonce'=>1, 'nc'=>1, 'cnonce'=>1, 'qop'=>1, 'username'=>1, 'uri'=>1, 'response'=>1);
    $data = array();

    preg_match_all('@(\w+)=([\'"]?)([a-zA-Z0-9=./\_-]+)\2@', $txt, $matches, PREG_SET_ORDER);

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

    return $needed_parts ? false : $data;
}
?>
   </programlisting>
  </example>
 </para>

 <note>
  <title>??????????</title>
  <para>
   ?ڱ?д HTTP
   ??ͷ????ʱ??????С?ġ?Ϊ?˶????еĿͻ??˱?֤?????ԣ??ؼ??֡?Basic???ĵ?һ????ĸ??????дΪ??B?????ֽ??ַ?????????˫???ţ????ǵ????ţ????ã??????ڱ?ͷ??
   <emphasis>HTTP/1.0 401</emphasis> ?У??? <emphasis>401</emphasis> ǰ???????ҽ???һ???ո???
  </para>
 </note>

 <para>
  ???????????У?????ֻ??ӡ???? <varname>PHP_AUTH_USER</varname> ??
  <varname>PHP_AUTH_PW</varname>
  ??ֵ??????ʵ???????У???????Ҫ???û??????????ĺϷ??Խ??м??顣???????????ݿ??IJ?ѯ???????? dbm ?ļ??м?????
 </para>

 <para>
  ע????Щ Internet Explorer
  ???????????????⡣???Ա?ͷ??˳???Ե??ƺ??е㴵ë???á?Ŀǰ?????ڷ???
  <literal>HTTP/1.0 401</literal> ֮ǰ?ȷ???
  <emphasis>WWW-Authenticate</emphasis> ??ͷ?ƺ????Խ????????⡣
 </para>

 <simpara>
  ?? PHP 4.3.0
  ????Ϊ?˷?ֹ????ͨ????д?ű??????ô?ͳ?ⲿ??????֤??ҳ???ϻ?ȡ???룬???ⲿ??֤???ض?ҳ????Ч??????&safemode;??????ʱ??PHP_AUTH
  ?????????ᱻ???á??????????Σ?<varname>REMOTE_USER</varname>
  ???Ա??????????ⲿ??֤???û??????˿?????
  <varname>$_SERVER['REMOTE_USER']</varname> ??????
 </simpara>

 <note>
  <title>????˵??</title>
  <para>
   PHP ???Ƿ??? <literal>AuthType</literal> ָ?????ж??ⲿ??֤?????Ƿ???Ч??
  </para>
 </note>

 <simpara>
  ע?⣬????Ȼ???ܷ?ֹ????ͨ??δ??֤?? URL ????ͬһ??????????֤?? URL ??͵ȡ???롣
 </simpara>
 <simpara>
  Netscape Navigator ?? Internet Explorer ?????????????յ? 401
  ?ķ????˷?????Ϣʱ???????еı????????????????? Windows
  ??֤???档???ܹ???Ч??ע??һ???û???????ʹ???????????????ǵ??û????????롣??Щ???????ַ?????ʹ??¼״̬?????ڡ?????????Ϊ??ע??????ť????Ӧ??Ϊ??
 </simpara>
 <para>
  <example>
    <title>ǿ???????????û??????????? HTTP ??֤?ķ???</title>
    <programlisting role="php">
<![CDATA[
<?php
  function authenticate() {
    header('WWW-Authenticate: Basic realm="Test Authentication System"');
    header('HTTP/1.0 401 Unauthorized');
    echo "You must enter a valid login ID and password to access this resource\n";
    exit;
  }

  if (!isset($_SERVER['PHP_AUTH_USER']) ||
      ($_POST['SeenBefore'] == 1 && $_POST['OldAuth'] == $_SERVER['PHP_AUTH_USER'])) {
   authenticate();
  }
  else {
   echo "<p>Welcome: {$_SERVER['PHP_AUTH_USER']}<br />";
   echo "Old: {$_REQUEST['OldAuth']}";
   echo "<form action='{$_SERVER['PHP_SELF']}' METHOD='post'>\n";
   echo "<input type='hidden' name='SeenBefore' value='1' />\n";
   echo "<input type='hidden' name='OldAuth' value='{$_SERVER['PHP_AUTH_USER']}' />\n";
   echo "<input type='submit' value='Re Authenticate' />\n";
   echo "</form></p>\n";
  }