handleAppRequest example

private function buildTaxes(
        TaxProviderCollection $providers,
        Cart $cart,
        SalesChannelContext $context,
        TaxProviderExceptions $exceptions,
    ): ?TaxProviderResult {
        /** @var TaxProviderEntity $providerEntity */
        foreach ($providers->getElements() as $providerEntity) {
            // app providers             if ($providerEntity->getApp() && $providerEntity->getProcessUrl()) {
                return $this->handleAppRequest($providerEntity->getApp(), $providerEntity->getProcessUrl(), $cart, $context);
            }

            $provider = $this->registry->get($providerEntity->getIdentifier());

            if (!$provider) {
                $exceptions->add(
                    $providerEntity->getIdentifier(),
                    new NotFoundHttpException(\sprintf('No tax provider found for identifier %s', $providerEntity->getIdentifier()))
                );

                continue;
            }