Lucia is an authentication library for SvelteKit that handle the bulk of the authentication process. It is bare-bone by design, allowing it to be used in many ways, but simple and straight forward enough to be easy to understand and to use. That said, it implements token theft detection, rotating refresh token, and silent refresh, to make sure your authentication system is secure.
It's important to note that this isn't an out-of-the-box authentication library. It does not validate the user's input nor does it not provide UI elements or OAuth authentication (though it can be implemented using Lucia). These are out of the scope of this library and is left up to you.
npm install lucia-sveltekit