🖥 SvelteKit Session Cookies: HttpOnly Cookies in SvelteKit #

In this video we look at using SvelteKit Session Cookies, continuing the series of videos which also covers Session Storage and Local Storage. We focus particularly on HttpOnly cookies which can be more secure than other cookies. That is because JavaScript code running in the browser has no access to them. The main benefit here is a decreased attack surface for cross site attacks. In the video we see how you might consider setting up a SvelteKit app where you need users to authenticate. We also see how you can expose client-safe fields stored in cookies to browser JavaScript using SvelteKit sessions.

If that sounds like something you can use, let's press play and crack on!

📹 SvelteKit Session Cookie: Video #

I should point out a small error in the video. The maxAge for a cookie should be specified in seconds. This is corrected in the hooks.js code below.

🖥 SvelteKit Session Cookie: Code #

 1import cookie from 'cookie';
 2const COOKIE_NAME = process.env['USER_COOKIE_NAME'];
 3 
 4export async function getSession(request) {
 5	if (request.locals.user) {
 6		return { user: request.locals.user };
 7	}
 8	return {};
 9}
10 
11export async function handle({ request, resolve }) {
12	const loggingOut = request.path === '/api/logout.json';
13 
14	const cookies = cookie.parse(request.headers.cookie || '');
15 
16	// before endpoint call
17	request.locals.user = cookies[COOKIE_NAME];
18 
19	// endpoint call
20	const response = await resolve(request);
21 
22	// after endpoint call
23	const user = loggingOut ? '' : request.locals.user;
24 
25	const secure = process.env.NODE_ENV === 'production';
26	const maxAge = 7_200; // (3600 seconds / hour) * 2 hours
27	const sameSite = 'Strict';
28	const setCookieValue = `${COOKIE_NAME}=${user || ''}; Max-Age=${maxAge}; Path=/; ${
29		secure ? 'Secure;' : ''
30	} HttpOnly; SameSite=${sameSite}`;
31 
32	return {
33		...response,
34		headers: {
35			...response.headers,
36			...(user || loggingOut ? { 'Set-Cookie': setCookieValue } : {})
37		}
38	};
39}

🔗 SvelteKit Session Storage: Links #

• Using Local storage with SvelteKit,
• Using Session storage with SvelteKit,
• Open full demo code repo on Github ,
• MDN Set-Cookie docs ,
• OWASP HttpOnly information ,
• SvelteKit session docs ,

🏁 SvelteKit Session Cookies: Summary #

What is an HttpOnly Cookie?

Http only cookies unlike Session Storage and Local Storage cannot be read by JavaScript code running in the browser. This brings security benefits, making HttpOnly cookies a preferred choice in many applications.

How can you share data between the client and server in SvelteKit?

SvelteKit has a session store. Client routes can access it via a named import from $app/stores. Once imported it can be read in a similar way to other stores. Session is not suitable for storing sensitive information.

How can sensitive information be sent from the server to the client in SvelteKit?

You can use HttpOnly cookies to send sensitive information, indentifying a user or session as well as session tokens. The client can send this data to the server with client requests, to process the sensitive data and respond with client-safe data. The server can access the data on the cookie, but client side JavaScript code cannot.

🙏🏽 Feedback #

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