If flask_oidc.registration register_client fails an empty client_secrets.json is created
In my setup I had to add the keycloak ip manually to the docker-compose file to allow ontodocker to connect to keycloak. That was hard to debug because after the registration failed for the first time, the empty client_secrets.json was already created [1] causing the ontodocker image to subsequently fail with a json decode error. Instead, the client_secrets.json should not be created to force ontodocker to create it on the next start.
[1] https://git.material-digital.de/apps/ontodocker/-/blob/master/flask_app/app/init.py#L45