[keycloak-user] token expired exception

Hi you, I just use keycloak for authen application to access my resource, but I don't know control token key life time. One app will not access my resource when token key is expired, this app does not know when reinit token key. I want to catch Token key expired to return apps. Please help me. Have any extend keylocak library? Goal of Keyloak is very good, I like this.