JSON Web Token is a proposed Internet standard for creating data with optional signature and/or optional encryption whose payload holds JSON that asserts some number of claims. The tokens are signed either using a private secret or a public/private key.
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.
The following diagram shows how a JWT is obtained and used to access APIs or resources:
1. The application or client requests authorization to the authorization server. This is performed through one of the different authorization flows. For example, a typical OpenID Connect compliant web application will go through the /oauth/authorize endpoint using the authorization code flow.
2. When the authorization is granted, the authorization server returns an access token to the application.
3. The application uses the access token to access a protected resource (like an API).
With JWT, authorization and authetication can be decoupled from the business logic.