public function col_operation($data) {
        $tokenpageurl = new \moodle_url(
            "/admin/webservice/tokens.php",
            [
                "sesskey" => sesskey(),
                "action" => "delete",
                "tokenid" => $data->id
            ]
        );
        return \html_writer::link($tokenpageurl, get_string("delete"));
    }