LOGIN SHELL WITH VALIDATION

<?php
error_reporting(0);
ob_start('ob_gzhandler');
session_start();

$username = 'user';
$password = 'root';

function pac($str) {
    echo $str;
}
pac('<html><head>
    <meta charset="UTF-8">
<title>Login</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
@import url("https://fonts.googleapis.com/css?family=Cabin");
*{
    padding: 0;
    margin: 0;
    box-sizing:border-box;
}
body {
    margin:auto;
    background: #191919;
    font-family: "Cabin";
    -webkit-font-smoothing:antialiased;
    font-size: 14px;
    color:#fff;
    text-shadow:0px 0px 0px #343436;
}
*:focus {
    outline: 0;
}
.container {
    max-width: 350px;
    margin: auto;
    background: none;
}
.content {
    margin:10px;
    background:#222;
    padding:7px;
    color:#fff;
    box-shadow:0px 1px 1px rgba(0,0,0,0.1) inset;
    border-radius:5px;
    max-width:350px;
}
input[type=text], input[type=password] {
    padding:7px;
    font-size:14px;
    font-family: "Cabin";
    width:100%;
    border:1px solid #343436;
    background:none;
    color: #FA5A5A;
}
input[type=text]:hover, input[type=password]:hover {
    border:1px solid #FA5A5A;
    transition: all 0.5s;
}
button {
    padding:7px;
    font-size:14px;
    font-family: "Cabin";
    background:#FA5A5A;
    width:100px;
    border:1px solid #FA5A5A;
}
button:hover {
    background:none;
    color:#FA5A5A;
    border:1px solid #FA5A5A;
    transition: all 0.5s;
}
.top5 {
    margin-top: 5px;
}
table {
    width:100%;
}
td {
    color:#fff;
    font-size: 14px;
 }
 a {
    text-decoration: none;
    color:#FA5A5A;
}
hr {
    border: 0;
    height: 1px;
    background-image: -webkit-linear-gradient(left, #FA5A5A, #FA5A5A, #FA5A5A);
    background-image: -moz-linear-gradient(left, #FA5A5A, #FA5A5A, #FA5A5A);
    background-image: -ms-linear-gradient(left, #FA5A5A, #FA5A5A, #FA5A5A);
    background-image: -o-linear-gradient(left, #FA5A5A, #FA5A5A, #FA5A5A);
}
h3 {
    font-weight:500;
}
</style></head></body>');
function form() {
    pac('<form action="" method="post">
    <table>
<td>Username :</td>
    <td><input name="user" type="text"></td><tr>
 <td>Password :</td>
    <td><input name="pass" type="password"></td>
    <tr>
    <td></td><td><button name="login">Login!</button></td></table>
    </form>');
}
pac('<script>
    baseUrl = window.location.href.split("?")[0];
    window.history.pushState("name", "?", baseUrl);
</script>');
if(isset($_GET['out'])) {
    setcookie('UNDERXPLOIT', time() - 3600);
    unset($_SESSION['username']);
}
pac('<div class="container">');
if(isset($_POST['login'])) {
if($_POST['user'] == $username AND $_POST['pass'] == $password) {
    $_SESSION['username'] = $username;
    $_COOKIE[$username] = $password;
    setcookie('UNDERXPLOIT', md5($_SERVER['HTTP_HOST']));
} else if(empty($_POST['user']) || empty($_POST['pass'])) {
    pac('<div class="content">Form Can\'t be  Empty !!</div>');
} else {
    pac('<div class="content">Invalid Username or Password !!</div>');
    }
}
pac('<div class="content"><center><br><h3>LOGIN</h3><br><hr><br></center>');
if($_SESSION['username'] == $username) {
    pac('Your Content Here ---> <a href="?out">./Logout</a><br>');
    } else {
        form();
    }
pac('<br><hr></div></div>');
?>