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

The part of this discussion I always stumble over is when it is recommended to "just" use anti-CSRF tokens. This is a non-trivial requirement. It is easy for one server -- most of them have built-in libs just like with JWT authentication. However, unlike JWT authentication it is a stateful process. So once you go beyond a single API server (including a fail-over scenario) you have to externalize the issued CSRF tokens into something like Redis (or a DB if you don't mind even more added latency). So all servers can be aware of the issued tokens. This adds another infrastructure piece that needs to be maintained and scaled for load. Edit: I guess people already using session servers are thinking "So what, we already have Redis to track user sessions." But with JWT, user sessions are stateless (just the token they provide and you validate) so this extra infrastructure isn't needed. That's a maintenance cost eliminated.

As far as local storage being vulnerable to XSS attacks, OWASP also puts out an XSS Prevention Cheat Sheet. The main attack vector for XSS is when you allow users to directly input HTML/JS and then execute it. Most major frameworks already santize user inputs to prevent this.

Modern JavaScript frameworks have pretty good XSS protection built in.

• OWASP XSS Prevention Cheat Sheet

The less common threat that you mentioned was NPM libraries becoming subverted to include XSS attacks. NPM has added auditing tools to report this and warn users. (Edit: Fair point is that people sometimes still use JS libs from CDNs, which may have less scrutiny.) And also Content Security Policy is supported in all major browsers and can prevent attacks and the exfil of token/data even if a script on your site gets compromised. It does not necessarily prevent the compromised script from making calls to your own API. But they would have to be targeting your API specifically to accomplish much.

I completely understand the recommendation to use cookies + Secure + HttpOnly + anti-forgery tokens from a security perspective. And as far as I am aware it is superior security to JWT in local storage. But it also has pretty significant constraints. And local storage is not bad, security-wise. It is isolated by domain. XSS attacks are already heavily mitigated by just using a modern JS framework and paying attention to NPM audit warnings. Throw in CSP for good measure. And of course not going out of your way to evaluate user-entered data as HTML/JS/CSS. (If your site functionality requires this, then you probably should use cookie auth and CSP.)

Great article. Thanks for the in depth research and clear tutorial. Logic was very concise. 😃

Was in a long search for this clarification.
Thanks

Thanks for this article, it helped me a lot!

If you use Express, then it could be worth looking at Express Session and the option to save the data to Redis:

app.use(
  session({
    name: 'sessionForApplication',
    secret: process.env.SESSION_SECRET,
    saveUninitialized: true,
    resave: true,
    cookie: {
      expires: expiryDate,
      domain: process.env.APP_DOMAIN
    },
    store: new RedisStore(optionsForRedis)
  })
)

Very descriptive and helpful article.
Thanks!!!

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?

I just wonder what is actually accessible by document.cookie?

Secondly would be the implementation. I am interested in all processes from highly-accessible sign-in, to protecting the API endpoint, and the server knows requesters' credentials (for attaching userId in database queries). I currently use Firebase / firebase-admin for these reasons, but I have trouble implementing storing token in cookies. I fear that it might be backend dependent...

I will consider your product.

Nice article, thank you! One thing I'm not sure I totally understood: About "Store your access token in memory and store your refresh token in the cookie". Doesn't that make us again vulnerable to XSS attacks? Because your in-memory token would be available by some injected javascript, no?

Hi, I am so excited about this article,
But what if the refresh token takes more than 4KB?
Is there any way to increase the space of Cookie?
Cookie is reling on the type of Browser?

I only signed up to leave a comment after landing here from a github issue.

I sent a random email to Kevin from the Cotter team a few months back asking for a feedback on something :) - I'd rather not go too specific..
And he was the one of the most friendliest & smartest person I ever met online - even though we had never met before.

Although our current project does not quite fit the bill for cotter usage(because we're a dApp and we have to use MetaMask for authentication), I'd definitely give cotter a shot if we had a chance. I can only imagine the product would be fantastic if smart, nice and hard-working people like Kevin had been working on it. And from my personal experience, I have learnt that the team matters as much as the product itself when choosing a Sass product.

Disclaimer: I have no ties with the cotter team. Just something out of my personal experience with one of the co-founders at Cotter.

You can use JWT localstorage and prevent CSRF attacks. When you are using a token bearer you are saying to the server that you only allow request with this token from the current browser client, so if a hacker stole the token, he can't make the request because the token are not coming from the original client. JWT is secure and for more security just config the life time of the token less than 8 hours.

This was concise yet effective article to understand the pros and cons of storing JWT in local storage/cookie. But I have a question.

In the firebase auth REST APIs, they are returning both accessToken and refreshToken in the response body. As per Option 3 in your article refresh token shouldn't be inside response. Refresh token should go to Cookie directly so that nobody can access through XSS. Why Google is doing that?

firebase.google.com/docs/reference...

Hi,
Is it possible to have explaination about that part:

Although a form submit to /refresh_token will work and a new access token will be returned, the attacker can't read the response if they're using an HTML form. To prevent the attacker from successfully making a fetch or AJAX request and read the response, this requires the Authorization Server's CORS policy to be set up correctly to prevent requests from unauthorized websites.

I do not understand the following part : "Although a form submit to /refresh_token will work and a new access token will be returned, the attacker can't read the response if they're using an HTML form"

To me, if the attacker manage to inject Javascript Code through XSS that will send an HTTP to /refreshtoken, then he will be able to read the response, thus retrieve the AccessToken and maybe send it to his malicious external server to us it.

Am I missing something? Thanks a lot !

Surely the vulnerability here is that you have a site vulnerable to XSS not the choice of where to store the token?