Variables not being passed to class method - php

Question

I'm building a login class with PHP, but the variables used are empty when I pass them to the class method even though they shouldn't be.
I tried returning only the $username variable but it's still empty, though if I return it without using the class I can see that it gets assigned correctly.
I'm using multiple other classes with methods where the variables gets assigned correctly.
I don't know if i've stared myself blind and am missing something obvious or if there's something else causing this.
class Auth
{
private $mysqli;
public function __construct(mysqli $mysqli)
{
$this->mysqli = $mysqli;
}
public function login($username, $password) //These variables are empty, even when they shouldn't be
{
$return['error'] = true;
$uid = $this->getUserId(strtolower($username)); //Returns false because $username variable is empty
if (!$uid) {
$return['message'] = 'No such user.'; //Output
return $return;
}
$user = $this->getUser($uid);
if (!password_verify($password, $user['password'])) {
$return['message'] = 'Password incorrect';
return $return;
}
$return['error'] = false;
$return['message'] = 'Logged in';
return $return;
}
private function getUserId($username)
{
$stmt = $this->mysqli->prepare("SELECT id FROM users WHERE username = ?");
$stmt->bind_param('s', $username);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($id);
if ($stmt->num_rows < 1) {
return false;
}
$stmt->fetch();
return $id;
}
private function getUser($uid)
{
$stmt = $this->mysqli->prepare("SELECT username, password, email FROM users WHERE id = ?");
$stmt->bind_param('s', $uid);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($username, $password, $email);
if ($stmt->num_rows < 1) {
return false;
}
$stmt->fetch();
$return['uid'] = $uid;
$return['username'] = $username;
$return['password'] = $password;
$return['email'] = $email;
return $return;
}
}
A form assigns the variables sent.
<form method="POST" action="post.php">
<label>Username
<input style="display:block;width:250px;" type="text" name="username" required></label>
<label>Password
<input style="display:block;width:250px;" type="password" name="password"></label>
<button style="display:block;" class="default_btn">Log in</button>
</form>
if (isset($_POST['username'])) {
$username = $_POST['username'];
$password = $_POST['password'];
$auth = new Auth($mysqli);
$auth->login($username, $password);
if ($auth->login()['error']) {
echo 'error:' . $auth->login()['message'];
} else {
echo 'success:' . $auth->login()['message'];
}
}
EDIT:
If I assign the variables in the class method the code works:
public function login($username = 'user', $password = 'pass')
But if I do this, it will not work:
$username = 'User';
$password = 'pass';
$auth = new Auth($mysqli);
$auth->login($username, $password);
Also, if I use the $_POST values outside of $auth->login() they are assigned so they are not empty when passing them to the class...

Answer 1

The problem seems to be that you don't store the result and instead call login again without values: if ($auth->login()['error']) {.
Try this:
<form method="POST" action="post.php">
<label>Username
<input style="display:block;width:250px;" type="text" name="username" required></label>
<label>Password
<input style="display:block;width:250px;" type="password" name="password"></label>
<button style="display:block;" class="default_btn">Log in</button>
</form>
if (isset($_POST['username'])) {
$username = $_POST['username'];
$password = $_POST['password'];
$auth = new Auth($mysqli);
$login_result = $auth->login($username, $password);
if ($login_result['error']) {
echo 'error:' . $login_result['message'];
} else {
echo 'success:' . $login_result['message'];
}
}