Creer un portfolio 2/5 WEBROOT prob de redirection

Bonjour, j'ai un petit souci de redirection (fin de la vidéo), après mon Log (ma connection)
je reste sur ma page login.php qui reste toute blanche, pareil pour logout.
j'utilise mamp ( sous domaine à la place de portfolio ( c'est studio)
http://localhost:8888/studio/login.php#
http://localhost:8888/studio/lib/auth.php#

Si quelqu'un sait m'aider!!

merci d'avance!

/**
* login.php
**/
<?php
$auth= 0; 
include 'lib/includes.php'; 

/**
* TRAITEMENT DU FORMULAIRE
**/
if(isset($_POST'username']) && isset($_POST'password'])){
        $username = $db->quote($_POST'username']);
        $password = sha1($_POST'password']);
        $select = $db->query("SELECT * FROM users WHERE username=$username AND password='$password'");

            if($select->rowCount() > 0){
                $_SESSION'Auth'] = $select->fetch();
                setFlash('connected');
                header('Location:' . WEBROOT . 'admin/index.php');
                die();
            }
}
/**
* INCLUSION DU HEADER
**/
include 'partials/header.php';
?>
<form action="#" method="post">
         <div class="form-group">
                <label for="username"> user </label>
                <?php echo input('username'); ?>
         </div>
         <div class="form-group">
                <label for="password"> password </label>
                <input type="password" class="form-control" id="password" name="password">
         </div>
         <button type="submit" class="btn btn-default"> connect </button>
</form>
<?php include 'lib/debug.php' ; ?>
<?php include 'partials/footer.php' ; ?>
/**
* auth.php
**/
<?php
session_start();
if(!isset($auth)){
    if (!isset($_SESSION'Auth']'id'])){
            header('location:' . WEBROOT . 'login.php');
            die();
  }
}
/**
* form.php
**/
<?php
function input($id){
    $value = isset($_POST$id]) ? $_POST$id] : '';
    return "<input type='text' class='form-control' id='$id' name='$id' value='$value'>";
}
/**
* constants.php
**/
<?php
define('WEBROOT', dirname($_SERVER'SCRIPT_NAME']) . '/');

/**
* includes.php
**/
<?php 
include 'constants.php';
include 'db.php';
include 'form.php';
// Session_start();
include 'auth.php';
include 'session.php';
?> 
/**
* logout.php
**/
<?php $auth = 0; 
include ('lib/includes.php');
$_SESSION = array();
header('Location:' . WEBROOT . 'index.php');
/**
* session.php
**/
<?php 
function flash(){
    if (isset($_SESSION'Flash'])) {
            extract($_SESSION'Flash']);
            unset($_SESSION'Flash']);
            return "<div class='alert alert-$type'>$message</div>";
    }
}
function setflash($message, $type = 'success'){
    $_SESSION'Flash']'message'] = $message;
    $_SESSION'Flash']'type'] = $type;
}