/**
* Signs user with given credentials
* @return string|null Either JWT either null if user is not saved
* @throws \yii\web\ServerErrorHttpException If getJWT method is missing in
* User model
*/
public function auth()
{
$user = User::findByUsername($this->username);
if ($user && $user->validatePassword($this->password)) {
return $user->jwt;
}
return null;
}
