Worked on the gchq/CyberChef repository to enhance the JWT Sign operation by introducing support for custom JWT headers, allowing fields such as kid and typ to be specified during token signing. This feature was implemented by updating the JWTSign class and expanding its test coverage to verify the new header functionality. The change improves interoperability with JWT-based authentication flows and key rotation scenarios by enabling standard header fields to be set as needed. The work was delivered as a focused feature update using JavaScript and Node.js, demonstrating skills in cryptography and full stack development within a collaborative open-source environment.