Hello,
you could add -debug flag to the standalone.sh command-line or define the following env variables in your docker container:
set DEBUG_MODE=true
set DEBUG_PORT=8787
this will start keycloak with remote debugging enabled by default on port 8787 which you need to expose on your docker container or use the container interface...
you can then connect to the keycloak instance inside the docker container via the remote debugger from your IDE.
For eclipse just go to "Debug configurations..." -> Remote Java Application -> select your project with the custom authenticator -> adjust hostname and port and click "debug".
Cheers,
Thomas