PHP user authentication PHP database-based user authentication code

<?php
/**
* 基于数据库的浏览器认证
* edit by bbs.it-home.org
*/

   function authenticate_user() {
      header('WWW-Authenticate: Basic realm="Secret Stash"');
      header("HTTP/1.0 401 Unauthorized");
      exit;
   }

   if (! isset($_SERVER['PHP_AUTH_USER'])) {
      authenticate_user();
   } else {
      mysql_pconnect("localhost","authenticator","secret")
      or die("连接数据库服务器失败!");
      mysql_select_db("java2s") or die("未能连接数据库!");

      $query = "SELECT username, pswd FROM user WHERE
      username='$_SERVER[PHP_AUTH_USER]' AND
      pswd=MD5('$_SERVER[PHP_AUTH_PW]')";

      $result = mysql_query($query);

      // 如果什么都没找到，则继续显示密码输入提示框
      if (mysql_num_rows($result) == 0) {
         authenticate_user();
      }
   }
?>