public static function type_config_form($mform, $classname = 'repository') {
        parent::type_config_form($mform);
        $key    = get_config('dropbox', 'dropbox_key');
        $secret = get_config('dropbox', 'dropbox_secret');

        if (empty($key)) {
            $key = '';
        }
        if (empty($secret)) {
            $secret = '';
        }

        $mform->addElement('text', 'dropbox_key', get_string('apikey', 'repository_dropbox'), array('value'=>$key,'size' => '40'));
        $mform->setType('dropbox_key', PARAM_RAW_TRIMMED);
        $mform->addElement('text', 'dropbox_secret', get_string('secret', 'repository_dropbox'), array('value'=>$secret,'size' => '40'));

        $mform->addRule('dropbox_key',    get_string('required'), 'required', null, 'client');
        $mform->addRule('dropbox_secret', get_string('required'), 'required', null, 'client');
        $mform->setType('dropbox_secret', PARAM_RAW_TRIMMED);
        $mform->addElement('static', null, '', get_string('instruction', 'repository_dropbox'));
        $mform->addElement('static', null,
                get_string('oauth2redirecturi', 'repository_dropbox'),
                self::get_oauth2callbackurl()->out()
            );

        $mform->addElement('text', 'dropbox_cachelimit', get_string('cachelimit', 'repository_dropbox'), array('size' => '40'));
        $mform->addRule('dropbox_cachelimit', null, 'numeric', null, 'client');
        $mform->setType('dropbox_cachelimit', PARAM_INT);
        $mform->addElement('static', 'dropbox_cachelimit_info', '',  get_string('cachelimit_info', 'repository_dropbox'));

    }