With a database session token system I could have a user login with a username/password, the server could generate a token (a uuid for example) and store it in the database and return that token to the client. Every request from thereon would include the token and the server would look up whether the token is valid and what user it belongs to.
Using JWT there would be no need to save anything to the database with respect to session/tokens thanks to the combination of the secret key kept on the server and the signed token the client keeps and sends with every request.
This is good but besides saving a database check each request (which would be fast anyway since it's just checking a hash table) it's not clear to me what the advantages are of using JWT. Can you anyone familiar with this explain? Let's ignore cookies, it's specifically a database custom token as described above and JWT that I am trying to compare and understand the benefits.
The main difference is the session storage size and lookup work required from the server:
On the server side, JWT stores a single key in memory (or in config file) - called secret key. That key has two purposes, it enables creating new encrypted tokens and it also functions like a master key that "opens all locks"- or in real life verifies all tokens. As a result the server responds much faster to auth requests, because it doesn't matter if you have two or two million users logged in - the same number of records (one, that server key) will be used to authenticate all client requests.
Traditional authentication that stores user sessions in a database, creates a record in the db for every single user, which results in multiple keys. So if you have two million users logged in, the server will create two million records and with each client request the server needs to locate the relevant session record in the database*.
JWT leaves it up to the client side to store and handle the entire session/user object. It actually makes much more sense because every client handles their own data only, so it doesn't cause heavy lifting for the client side either.
As for what you wrote in your last paragraph, it's not just db calls that we save here. JWT is actually much more scalable because of its independent and lightweight nature, it doesn't fail as auth requests pile up and it allows the server to handle auth accross devices and services without managing sessions on the server side.
Security wise though, db sessions arguably have the upper hand: they can be more secure because of that latency, and are also less vulnerable to session hijacking after user logout.
*The db stored sessions method can be optimized with effective caching and by storing only the session id (as opposed to the entire user object) in a fast key/value server such as Redis. That said, I would still choose JWT method over db for most cases.
A Json based token(JWT) overcomes the following problems:
- Mobile issues: Native mobile apps seems to have problems working with cookies so if we need to query a remote API, maybe session auth is not the best solution.
- CSRF issues: If you are following cookies way then you need to have CSRF to avoid cross site requests.
But JWT doesn’t use sessions, has no problems with mobile, it doesn’t need CSRF and it works very well with CORS too. If you dont have a valid token you can't do anything.
One more as this token gets stored at client local storage/session storage so you can pass these tokens to other clients as well but you have to share the same credential which you used to generate this JWT.
来源：https://stackoverflow.com/questions/26216489/json-web-token-jwt-benefits-over-a-database-session-token