oauth 2.0 - Why JWT is a stateless authentication?

Question

I am trying to understand how JWT authentication is stateless. In stateful authentication, there will be a session id. Here there is a JWT token which is signed. So the authentication server issues the JWT token, but can I say the validation of the JWT token in subsequent requests are done by the endpoint server (application server) rather than the authentication server. I believe this is possible as JWT is signed with expiry date (and also some other information) and the public certificate of authentication server is available to all endpoint servers.

So the authentication server will be only responsible for issuing the tokens and not validation. The validation will be done by the endpoint server.

Is my understanding correct? Is this how JWT is made stateless? Otherwise, I don't see how it is different from a stateful authentication as both can be implemented using tokens.

In stateful authentication, the centralized server will be responsible for issuing the tokens as well as validation is each request.

Answer 1

JSON Web Tokens (JWT) are referred to as stateless because the authorizing server needs to maintain no state; the token itself is all that is needed to verify a token bearer's authorization.

JWTs are signed using a digital signature algorithm (e.g. RSA) which cannot be forged. Because of this, anyone that trusts the signer's certificate can safely trust that the JWT is authentic. There's no need for a server to consult the token-issuing server to confirm its authenticity.

Notice in this diagram that the Resource Server does not need to check back with the Authorization Server:

_{Source: https://jwt.io/introduction/}