Protocol mapper for client assertions provided during client authentication with self-signed JWT


Is it possible with the built-in protocol mappers to retrieve client assertions (e.g. client-provided claims in a self-signed (HMAC/private key) JWT)

and include them into the outgoing ID/access token?

If not, is it possible in a custom protocol mapper? From the Keycloak code, I cannot figure out if the content of the authentication JWT is stored in the session.