https://github.com/ory/ladon is an option. Essentially, it imposes a lot of the fine-grained access control model on you, but then it's up to you to implement the actual database/business-logic layer [1] as well as the API layer to actually expose the service.
[1] You do so by implementing this interface: https://github.com/ory/ladon/blob/master/warden.go