怎么在这个文件中实现保存账号密码并写入到一个文件中

如何在这个文件中实现保存账号密码并写入到一个文件中？

PHP code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--><?require_once ("php/report/include/cookie.php");$domain = trim($_SERVER["SERVER_NAME"]);if(file_exists("/var/eyou/apache/htdocs/".$domain)){    include("$domain");    exit;}?><title>青岛职业技术学院电子邮件系统</title><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><script language="javascript" src="/js/jquery-1.2.6.js"></script><style type="text/css"><!--.font{    font-family: Arial, Helvetica, sans-serif;    font-size: 12px;    color: #4c4c4c;}.input {    font-family: Arial, Helvetica, sans-serif;    font-size: 12px;    color: #4c4c4c;}body{    margin: 0px;}.message{    color:red;    font-family: Arial, Helvetica, sans-serif;    font-size: 12px;}--></style><script language="javascript">$(document).ready(function() {    $("#submit").click(function(){        login();        return false;    })});function login() {    var messageDefault = "绯荤</script>