login with php but the user data comes from a csv file

I want to extract my user data from a csv file, pack it into an array and then check whether the user’s input matches data from the csv file

This is my previous code:

<?php
session_start();

$handle = fopen('users.csv', 'r');
while (($csv_array = fgetcsv($handle, NULL)) !== false) {
    foreach ($csv_array as $index) {
    }
    if (isset($_POST['vorname']) && isset($_POST['nachname']) && isset($_POST['mail']) && isset($_POST['passwort'])) {
        $vorname = $_POST['vorname'];
        $nachname = $_POST['nachname'];
        $mail = $_POST['mail'];
        $pw = $_POST['passwort'];

        if ($vorname == $index['vorname'] && $nachname == $index['nachname'] && $mail == $index['mail'] && $pw == $index['passwort']) {
            $_SESSION['vorname'] = $vorname;
            $_SESSION['nachname'] = $nachname;
            $_SESSION['mail'] = $mail;
            $_SESSION['passwort'] = $pw;
            header("Location: account.php");
        }
    }
}

fclose($handle);

?>

ps: i dont use a database for this