<form method="POST" action="verification.php" class="loginFields">
<input type="text" name="username" placeholder="Username" autofocus>
<input type="password" name="password" placeholder="Password">
<input type="submit" name="submit" value="Inloggen">
</form>

// Start new DOMDocument and load html file.
$dom = new DOMDocument();
libxml_use_internal_errors(true);
$dom->loadHTMLFile("loginHTML.html");
libxml_use_internal_errors(false);

// Haal verification.php op om gegevens te checken.
include_once('verification.php');


if(isset($_POST['submit'])){
    $username = $_POST['username'];
    $password = $_POST['password'];

    $object = new user();
    $object->login($username, $password);
}
// Save DOMDocument with html document.
echo $dom->saveHTML();

// Include connection.php om connectie te maken te de database.
include_once('inc/connection.php');
include_once('login.php');

class user{

    private $db;

    public function __construct(){
        $this->db = new connection();
        $this->db = $this->db->dbconnect();
    }


    public function login($username, $password){
        $this->db = new Connection();
        $this->db = $this->db->dbConnect();

        // Als $username en $password gevuld zijn checken op overeenkomst
        if(!empty($username) && !empty($password)){
            $st = $this->db->prepare("SELECT * FROM users WHERE username=? AND password=?");
            $st->bindParam(1, $username);
            $st->bindParam(2, $password);
            $st->execute();
            $result=$st->fetch(PDO::FETCH_ASSOC);
            $id=$result['id'];

            // Als er een overeenkomst is doorsturen naar admin.php en session aanmaken
            if($st->rowCount() == 1) {
                $_SESSION['id'] = $result['id'];
                $_SESSION['ingelogt'] = $username;
                header('location: admin.php');
                exit;
            } else {
                echo "Incorrect username or password";
            }

        // Als er niks is ingevoerd bij het inlogscherm
        } else {
            echo "Please enter your username and password";
        }
    }
}

session_start();
// If session is not ingelogt lead back to index.php.
if(!isset($_SESSION['id'])) {
    header("location: index.php");
    die();
}

//...
$st->execute();
$row = $st->fetch();

$id = $row['id'];