This project is not currently in a state where it would be useful to give usage advice. The code will evolve quickly and break often, if you are interested in using this, I am afraid you will have to look at the code and know what you are doing.
That being said, as soon as this reaches a sort of stable state I will add information here.
Currently expects that Open Policy Agent is serving group mappings on http://localhost:8181/v1/data/app/rbac/get_groups. Run opa run --server example.rego in the repo folder to test an initial example.
If you want to override this default you can do this by defining a fully qualified opa uri (including rule) in the env var NIFI_OPA_URI.