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

<!--

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-->
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>