private function askForCustomResources(InputInterface $input, OutputInterface $output) {
        $question = new Question(
            'Which custom resources should the public key have access to?' . PHP_EOL .
            '(comma-separated) '
        );

        $question->setValidator(function($answer) {
            $resources = array_filter(array_map('trim', explode(',', $answer)));

            if (empty($resources)) {
                throw new RuntimeException(
                    'You must specify at least one resource'
                );
            }

            return $resources;
        });

        return $this->getHelper('question')->ask($input, $output, $question);
    }