Redirect user from a custom access callback

Question

In my module routing I have a custom access callback for a payment page.

_custom_access: 'Drupal\mymodule\Form\PaymentForm::access'

It checks if the user:

• is allowed to make the payment (it's their own)
• actually needs to (has it already been paid)

It works fine, but in the latter case, whilst I can give them an explanatory warning:

\Drupal::messenger()->addWarning('Fee already paid or no fee to pay.');
return AccessResult::forbidden();

it'd be nicer to redirect them to a page that's friendlier than:

Access Denied - you are not authorised to access the page.

Drupal / Symfony insists on returning something that implements AccessResult - so I can't return a RedirectResponse. Any suggestions? Moving the checks to buildForm() seems a bad idea.

Answer 1

For the second condition an access denied doesn't seem to be the right answer because permissions are not the reason. It is to control the business logic and for this I think it is a good idea to use buildForm(), which acts in a form route as a controller from which you can return a redirect response:

  public function buildForm(array $form, FormStateInterface $form_state) {
    if (...) {
      $this->messenger()->addMessage('Fee already paid or no fee to pay.');
      return $this->redirect('<front>');
    }

    // build form if fee is not paid already

  }