Token introspection
Token introspection interface provides one method, that helps you ask the OAuth2 provider details about the token. The response is described in rfc7662 section 2.2. The only guaranteed field is active that determines if the token is still valid.
The oauth2-cache-cats module provides the cached version of this interface CachingTokenIntrospection that allows you to limit the calls to the OAuth2 provider. To use it you need to provide regular TokenIntrospection, the cache implementation and the default expiration time, since the introspection response doesn't necessarily provide such information.
The cache implementation can be anything that implements ExpiringCache trait, for the out of the box solution use CatsRefExpiringCache, but keep in mind the memory consumption - that instance doesn't limit the list of tokens kept.