[moyok]

The point is that it would reduce the DB/cache load, as the refresh token would need to be verified once in a few minutes or so as opposed to verifying it for every request. Regular requests could be authenticated in the CPU itself without having to go through to the DB/cache layer. This means lower latency and reduced load on the DB/cache.

[madeofpalk]

...then make the JWT last as long as the refresh token.

[moyok]

If the JWT is as long as the refresh token, then what's the point of having a refresh token? You would then probably need to get new refresh tokens then to make the session last longer.

The idea is to make the refresh token last for say a few days, and the JWT for say 10 minutes. Now, every 10 minutes the client needs to use the refresh token to get a new JWT. The maximum time a client can have access to the service without a valid refresh token is 10 minutes. All the requests made in this window of 10 minutes would be deemed authenticated by verifying the JWT, and without having to go through the database or cache.

Now, say a user of a web app clicks "log me out from all my devices". The user's access needs to be revoked from everywhere they are logged in. If you invalidate all their refresh tokens, then in a max of 10 minutes they would be logged out from everywhere, as their refresh tokens would no longer work and the JWT duration is only 10 minutes.

This approach is essentially a mid-way or a tradeoff between using traditional sessions and JWT. "Pure" JWT is stateless and hence cannot support individual session revocation. The only way to invalidate sessions in "pure" JWT would be to invalidate the key or certificate used to sign the JWT, but that would invalidate everyone else's sessions as well and hence is not very practical.

Since with this approach you implement sessions plus JWT, it's more complicated than just using sessions. JWT should be used for such applications when the latency or load benefit is significant enough to justify the added complexity. For applications that do not need session revocation, however, JWTs are a convenient way to implement sessions without needing a DB or cache layer.