Auth_HTTP认证的问题,请指教谢谢!

安装pear,安装目录为C:\Program Files\PHP\PEAR
拷贝了一个书上的例子运行,但运行时出现如下致命错误:
Fatal error: Class 'Auth' not found in C:\Program Files\PHP\PEAR\Auth\HTTP.php
on line 54
但我看了一下HTTP.php中require_once "Auth/Auth.php";
并且
C:\Program Files\PHP\PEAR\Auth\Auth.php中也有Auth.php的定义了.

请问是什么原因?

通过phpinfo()函数,include_path设置如下:
include_path .;C:\Program Files\PHP\pear

尝试修改HTTP.php中的require为require_once "Auth.php";无效.

<?php
    require_once("Auth/HTTP.php");
   // Designate authentication credentials, table name,
   // username and password columns, password encryption type,
   // and query parameters for retrieving other fields
   $dblogin = array (
      'dsn' => "mysql://corpweb:secret@localhost/corporate",
      'table' => "userauth",
      'usernamecol' => "username",
      'passwordcol' => "pswd",
      'cryptType' => "md5",
      'db_fields' => "*"
   );

  // Instantiate Auth_HTTP
  $auth = new Auth_HTTP("DB", $dblogin) or die("blah");
  // Begin the authentication process
  $auth->start();
  // Message to provide in case of authentication failure
  $auth->setCancelText('Authentication credentials not accepted!');
  // Check for credentials. If not available, prompt for them
  if($auth->getAuth())
  {
     echo "Welcome, $auth->commonname<br />";
  }
?>