[keycloak-user] how to intercept/flow: VerificationException: Token is not active

[java_os]

Hi
I have 2 bearer rest layers (A,B): A calls B. In front I have an angular
web layer calling A -> B.

What is the best practices to handle "Token is not active" when user sits
in front idle and token becomes inactive, http session still valid but KC
token expired? If B reaches token not active, on the call from A to B -
how would I propagate this to the front layer?
A has to consume the ValidationException from B and notify front layer to
auto logout or prompt the user with a message saying 'your session
expired, please login' or automatically throw the user into the login
prompt in front.

For this scenario above, anyone share some thoughts?
Thanks