What solutions are there to invalidate jwt tokens (jwt access tokens) when a user logs out?

What solutions are there to invalidate jwt tokens (jwt access tokens) when a user logs out?

Daily short news for you
  • For a long time, I have been thinking about how to increase brand presence, as well as users for the blog. After much contemplation, it seems the only way is to share on social media or hope they seek it out, until...

    Wearing this shirt means no more worries about traffic jams, the more crowded it gets, the more fun it is because hundreds of eyes are watching 🤓

    (It really works, you know 🤭)

    » Read more
  • A cycle of developing many projects is quite interesting. Summarized in 3 steps: See something complex -> Simplify it -> Add features until it becomes complex again... -> Back to a new loop.

    Why is that? Let me give you 2 examples to illustrate.

    Markdown was created with the aim of producing a plain text format that is "easy to write, easy to read, and easy to convert into something like HTML." At that time, no one had the patience to sit and write while also adding formatting for how the text displayed on the web. Yet now, people are "stuffing" or creating variations based on markdown to add so many new formats that… they can’t even remember all the syntax.

    React is also an example. Since the time of PHP, there has been a desire to create something that clearly separates the user interface from the core logic processing of applications into two distinct parts for better readability and writing. The result is that UI/UX libraries have developed very robustly, providing excellent user interaction, while the application logic resides on a separate server. The duo of Front-end and Back-end emerged from this, with the indispensable REST API waiter. Yet now, React doesn’t look much different from PHP, leading to Vue, Svelte... all converging back to a single point.

    However, the loop is not bad; on the contrary, this loop is more about evolution than "regression." Sometimes, it creates something good from something old, and people rely on that goodness to continue the loop. In other words, it’s about distilling the essence little by little 😁

    » Read more
  • Alongside the official projects, I occasionally see "side" projects aimed at optimizing or improving the language in some aspects. For example, nature-lang/nature is a project focused on enhancing Go, introducing some changes to make using Go more user-friendly.

    Looking back, it resembles JavaScript quite a bit 😆

    » Read more

Problem

Authenticating users through token-based authentication is becoming increasingly popular as the client-server model is widely used. While session or cookies were commonly used to identify user sessions in the past, now we have another option which is token-based authentication, especially jwt.

Jwt is a string used for identification, usually the user's login session. Jwt works by digitally signing the attached token payload for authentication.

For example, if we need to store basic information to identify a user:

{
    "user_id": 1,  
    "role": "user",  
}

Jwt will encode that information along with a "signature", which can only be verified by the server. A valid jwt also means the accompanying information is accurate.

In the jwt, the exp attribute is the expiration time of the token. A signed token will have an expiration time. The token becomes effectively invalidated after that time. Jwt is designed to reduce querying the database for identity information. The server only needs to authenticate the token and retrieve the necessary information.

Therefore, jwt is only truly invalidated when the exp has expired. So how do we revoke a jwt token when a user logs out? Since logging out essentially means ending the session, the token must no longer be valid.

Simply delete the token from the browser

Clearly, this method does not have any effect on server-side security, but it is the simplest approach. When applying this method, pray that hackers do not get hold of your token before you log out. Just kidding, you should only apply this method when security is not too strict.

Create a blacklist

You can store invalid tokens until their signed expiration date and compare them with incoming requests.

However, this seems to break the principle of not querying the database from the beginning, as you will need to query the database for every request.

But the storage data may be lower, as you only need to store the tokens that users have logged out of.

This method also brings a major risk as you are still unsure if the token was stolen before you logged out. Or suppose before making the logout request, the client had an error and couldn't query, but it already deleted the data on the client, causing the token to not really be added to the blacklist on the server.

Keep token expiration time short and refresh them frequently

If you have heard of refresh tokens, this is the method that uses refresh tokens to reduce the expiration time of the tokens to the lowest possible.

Keeping the expiration time of the token short makes the token only exist for a short period of time, forcing the use of a refresh token to obtain a new token and keep rotating like that. If the token or refresh token is leaked, we can simply add that refresh token to the blacklist. This also helps reduce the storage data in the blacklist compared to keeping the access token.

So what should we do when a user's token is found to have leaked?

In any case, be prepared to face a user's token being leaked and you have to handle them. The simplest solution is to invalidate the identifier id stored in the token's payload. For example, if the payload you sign for the token includes:

{
    "user_id": 1,  
    "role": "user",  
}

Then change the id of the user to 1 in the database. Or if it is serious, change the secret used to sign the token to immediately invalidate all issued tokens.

Anyway, this method is only a last resort. What I want to say is, be prepared with backup plans to deal with token leaks at any time. Jwt is designed to reduce server load, but consider the trade-off between performance and security.

Summary

Access Token is a string used to identify a user's session. When the access token is a token created according to the jwt standard, we can identify the user without querying the database. Every jwt token comes with an expiration time, and if it is leaked or handled incorrectly when the user logs out, the user's data is vulnerable to attacks. Therefore, be cautious when handling tokens when a user logs out, and have contingency plans to deal with token leaks at any time.

Premium
Hello

Me & the desire to "play with words"

Have you tried writing? And then failed or not satisfied? At 2coffee.dev we have had a hard time with writing. Don't be discouraged, because now we have a way to help you. Click to become a member now!

Have you tried writing? And then failed or not satisfied? At 2coffee.dev we have had a hard time with writing. Don't be discouraged, because now we have a way to help you. Click to become a member now!

View all

Subscribe to receive new article notifications

or
* The summary newsletter is sent every 1-2 weeks, cancel anytime.

Comments (1)

Leave a comment...
Avatar
Thành Đỗ2 years ago

Giữ thời gian hết hạn của token trong khoảng thời gian ngắn và làm mới chúng thường xuyên - không hiểu tại sao phải làm thế này trong khi xss có thể lấy được luôn refresh token rồi

Reply
Avatar
Xuân Hoài Tống2 years ago

Bạn nói đúng có thể lấy đc refresh token nhưng mục đích của refresh token là giữ cho access token có thời gian hết hạn ngắn nhất có thể, nếu chẳng may bị lộ bạn có thể block refresh token thay vì rất nhiều access token có thời gian hết hạn lâu dài mà bạn tạo ra

Avatar
Thành Đỗ2 years ago

Ý mình là hacker vẫn lấy được refresh token ấy