UNSAFE php-user-authentication/controllers/login.php /

[Raisel]

for things like that I gave up on third-party classes, making your own should be safer, since only you can know where there is a hole in the code ...

ln17: $sql = "SELECT * From users WHERE email = '{$email_signin}' ";
I think it should be
$sql = "SELECT * From users WHERE email = '{$user_email}' ";

see how it is today:

if(isset($_POST['login'])) {
$email_signin = $_POST['email_signin'];
$password_signin = $_POST['password_signin'];

    // clean data 
    $user_email = filter_var($email_signin, FILTER_SANITIZE_EMAIL);
    $pswd = mysqli_real_escape_string($connection, $password_signin);

    // Query if email exists in db
    $sql = "SELECT * From users WHERE email = '{$email_signin}' ";
    $query = mysqli_query($connection, $sql);
    $rowCount = mysqli_num_rows($query);