    public function validateInputSource($fields)
    {
        if (!empty($this->data['Feed']['input_source'])) {
            $localAllowed = empty(Configure::read('Security.disable_local_feed_access'));
            $validOptions = array('network');
            if ($localAllowed) {
                $validOptions[] = 'local';
            }
            if (!in_array($this->data['Feed']['input_source'], $validOptions)) {
                return __(
                    'Invalid input source. The only valid options are %s. %s',
                    implode(', ', $validOptions),
                    (!$localAllowed && $this->data['Feed']['input_source'] === 'local') ?
                    __('Security.disable_local_feed_access is currently enabled, local feeds are thereby not allowed.') :
                    ''
                );
            }
        }
        return true;
    }