Which JWT parameter should include a nonce to prevent replay attacks in microservices?

The correct choice is the jti claim, which stands for "JWT ID." This parameter is specifically designed to provide a unique identifier for each JWT, essentially serving as an anti-replay mechanism. By including a nonce, or a randomly generated token, in the jti claim, you can ensure that each JWT is unique and can only be used once.

This prevents replay attacks, where an attacker could intercept a JWT and attempt to use it again after its initial use. By validating that the jti claim's value has not been previously seen or used, a microservice can effectively mitigate the risk of such attacks. This approach adds an additional layer of security in microservices architecture by ensuring that each token is fresh and not reusable.

Other claims such as the iss (issuer), exp (expiration), and sub (subject) serve different purposes: the iss claim identifies who issued the token, the exp claim determines the token's expiration time, and the sub claim identifies the subject of the token. While all these claims contribute to the overall security and usability of a JWT, none of them are specifically intended to prevent replay attacks, which is the primary function of the jti claim when utilized appropriately.