What does it mean when a JWT is properly validated?

When a JSON Web Token (JWT) is properly validated, it signifies that the server confirms the token was signed using the correct algorithm and key. This is critical because a JWT includes claims that can be trusted only if it has been signed by a trusted source. The signing process ensures that the information contained within the token has not been altered. When the server receives a JWT, it must verify that it was signed using the appropriate algorithm and key combination that the server expects. This process is essential to prevent attacks such as forgery or replay, thereby ensuring the integrity and authenticity of the information communicated in the token.

The other options do not accurately reflect the validation process of a JWT. For instance, while keeping the token client-side might enhance application functionality, it does not relate directly to the validation of the token itself. Similarly, the assertion about an attacker being unable to manipulate encryption methods overlooks the need for proper signing and verification; it is not solely about encryption. Lastly, the user verifying their own token without server involvement contradicts the essence of JWT validation, which relies on server-side checks to ensure that the token was genuinely issued and signed by a trusted authority.