[keycloak-user] accessing client JWT token in token mapper when using signed JWT authenticator.

[Billiet Tom]

Hi,

I'm currently trying to create a Mapper for a client that uses "Signed JWT" as the client authenticator. In the mapper I would like to access some fields from the JWT token that's used to authenticate the client.

I cannot figure out a way to do so. I've tried to create a custom mapper that extends AbstractOIDCProtocolMapper, but I don't seem to be able to access the client JWT token anywhere.
When digging somewhat deeper, I think the JWTClientAuthenticator (https://github.com/keycloak/keycloak/blob/master/services/src/main/java/org/keycloak/authentication/authenticators/client/JWTClientAuthenticator.java) should expose this if I want to be able to use it later in a mapper. If the JsonWebToken would be stored on the userSession note object that would be possible.
But that  would require a feature request to have this exposed. Is there another way to make this possible?

Thanks,
Tom