How to throw custom errors for 401 and 403 using springboot and keycloak?

Hello, I am following Keycloak’s guide to secure Springboot rest api (keycloak-quickstarts/app-authz-rest-springboot at latest · keycloak/keycloak-quickstarts · GitHub). Keycloak is throwing only error codes. I am trying to add a message into that errors. Need Guidance to solve the issue. Thanks in advance.