Cookie signing powered by SK

Describe the problem

I can see examples on the web where raw userId is used as session key: https://dev.to/theether0/sveltekit-changes-session-and-cookies-enb

cookies.set('session', user.entityId, {
            path: '/',
            httpOnly: true,
            sameSite: 'strict',
            secure: !dev,
            maxAge: 60 * 60 * 24 * 30
        });

export const handle: Handle = async ({ event, resolve }) => {
    const session = event.cookies.get('session');
    // ...
    const currentUser = await userRepository.fetch(session as string);
    // ...
}

Describe the proposed solution

Cookies should be signed by default, or the option to sign cookies should be integrated in SK.

Alternatives considered

No response

Importance

would make my life easier

Additional Information

No response

Start by tracing the cookies.set and event.cookies.get APIs shown in the issue through the SvelteKit repository. No repository files or tests are named, so identify the cookie implementation and its existing test coverage before deciding whether signing is a default behavior or an opt-in API. Done should include a defined signing interface and coverage for signed cookie creation and retrieval.