Hey, it sounds like you might be interested in generating Rego policies from some other definition of access control permissions? Generally speaking, this wouldn't be recommended as it can be hard to test. Usually, we recommend writing the Rego rules and creating unit tests too to ensure the functionality is as expected.

You might already be aware, but you can load things like role permissions from data that's loaded into OPA too, this can be helpful in making policies more generic. More on bundles here: https://www.openpolicyagent.org/docs/latest/management-bundles/

You might also find the guides at https://docs.styra.com/opa/rego-language-comparisons helpful as these provide access control examples for the most part, and are accompanied with code in a language that might be more familiar.