NarKampenTake2/ServerFiles/CheckUsername.php

<?
$HOST = 'nordh.xyz';
$USERNAME = 'narKampen';
$PASSWORD = '9Bq.6[AcTc2ADwN-';
$DATABASE = 'narKampen';
$PORT = '3306';

$secretKey = 'TheNarKampenSecretKey';

try {
    $dbh = new PDO(
        'mysql:host=' . $HOST . ';dbname=' . $DATABASE,
        $USERNAME,
        $PASSWORD
    );
} catch (PDOException $e) {
    echo '<h1>An error har occured. </h1><pre>', $e->getMessage(), '</pre>';
}

$sth = $dbh->prepare('SELECT * FROM User WHERE username = :username');
try {
    $sth->execute($_GET);
} catch (Exception $e) {
    echo "<h1>An error has occured. </h1><pre>", $e->getMessage(), '</pre>';
}
$sth->setFetchMode(PDO::FETCH_ASSOC);

$result = $sth->fetchAll();

if (count($result) > 0) {
    echo true;
} else {
    echo false;
}