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re: LocalStorage vs Cookies: All You Need To Know About Storing JWT Tokens Securely in The Front-End VIEW POST

FULL DISCUSSION
 

Hi Michelle, really great article!
What always confused me about httpOnly cookies and JWT is that the frontend app is missing a big benefit of JWT, which is the payload containing claims and possibly other custom data from the backend.
This is most often the user's role, which then the app uses to render privileged parts of the UI and so on, or the token expiry information. With httpOnly, this benefit is not utilised - but the cost in increased packet size is still being paid!
There are strategies which take option 3 to the extreme, and people have already written great articles about this in details, that the JWT token itself should be split into 2 parts, it's signature in httpOnly, and the rest in a normal JS-accessible cookie. This ofcourse increases the complexity of the backend as well, which now needs to piece together the final JWT from two different incoming sources. I guess this could be option 4.

It seems to me, that in order to make good secure use of JWT, considerable complexity on both stacks must be considered. Alternatives are either insecure, or not utilizing the benefits of JWT, which would then just be better off using bearer tokens.

Again, thanks for the great article. It really got me thinking about these things and I think a great discussion could be made about the topic.

What is your take on splitting the token into two cookies? Does the added complexity justify the security gained?

 

Hi Marko, Putri here – Michelle's cofounder.

That's an interesting suggestion! I don't quite understand how the frontend would miss being able to read the claims/custom data in the JWT using option 3. By storing the access token in memory, you can decode and read the claims in the frontend whenever the access token is available. When the access token is not available in memory (after a refresh/change tab), you can use a function that will refresh the access token, and now you have the access token available again in memory and you can read/decode it in the frontend.

Splitting the JWT might be a useful option if the above solution doesn't help. Let me know what you think :)

 

By storing the token in memory, you risk compromising it by means of xss. The damage is contained since the token is short-lived, but still a window of opportunity exists.
We can either accept this risk or add considerable complexity to reduce it. What do you think?

That's true, storing in memory is still prone to XSS attack, it's just harder for the attacker to find it than localStorage.

Splitting the JWT into 2 cookies where the signature is in an httpOnly cookie, but the rest of the JWT is accessible to JavaScript makes sense. This means that the frontend can still access JWT except for the signature.

I think it's up to the website to determine what kind of attack factor that they're trying to mitigate against to decide whether they need the upgrade in security.

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