$username = $_POST['username_login'];
$password = $_POST['password_login'];
$fields = 'cust_id, cust_fname, cust_lname, cust_password';
$sql = "select $fields from customers where cust_username = ";

if (user_exists($username))
{
    $sql .= "'" . $username . "'";
    $results = $db_conn->query($sql) or die($db_conn->error);
    $results = $results->fetch_assoc();
    $hash = $results['cust_password'];

    if (password_verify($password, $hash))
    {