Keystone role assignments backend plugin OpenFGA

This project implements a backend plugin for Keystone to manage role assignments not in the Keystone database, but in the OpenFGA.

It is expected that every role assignment in Keystone context is represented by a relation in the OpenFGA (ReBAC) between user/group and project/domain.

model
  schema 1.1

type domain

type user
  relations
    define owner: [domain]

type group
  relations
    define member: [user, group#member]
    define owner: [domain]

type project
  relations
    define admin: [user, group#member]
    define manager: [user, group#member] or admin
    define member: [user, group#member] or admin or manager
    define owner: [domain]
    define reader: [user, group#member] or member or admin
    define service: [system]

type system
  relations
    define admin: [user, group#member]
    define member: [user, group#member] or admin
    define reader: [user, group#member] or member or admin
    define system: [user, group#member]

Delegating role assignments to the OpenFGA allows to improve integration of OpenStack with the external IdP and authorization system to centrally manage user authorizations for different service providers (improves service provider role of OpenStack).

Installation

For the moment the project is not being published to the PyPi so you can install it from git repository.

Install the project into the virtual environment with the Keystone using pip install .

Configuration

In order to enable the integration it is necessary to make few changes in the keystone.conf

[fga]
api_url = <OPEN_FGA_URL>
store_id = <OPENFGA_STORE_ID>
model_id = <OPENFGA_MODEL_ID>

...

[assignment]
driver = openfga

Additional considerations

1. OpenFGA must be highly available. In this deployment style OpenStack will query OpenFGA for at least every authentication request.
2. Having many roles requires expanding OpenFGA authorization model to define every role as a relation. This is not very scalable but at the same time unavoidable due to the nature of role assignments in OpenStack being a triplets (actor-role-object).
3. Keystone and OpenFGA both have methods of inheriting/inferring roles through role inference, group membership, domain to project delegation and so on. Currently Keystone does not support delegating such decisions to the backend and instead reimplements it internally. This has an effect that when certain role is granted between assignee and the object it is not possible to learn how is this achieved (as a direct assignment of through inheritance). It is strongly advised to keep role inference and user/group relations in sync between Keystone and OpenFGA to reduce confusion.
4. Keystone uses aggressive caching on the provider level. Due to that the driver code might not be even invoked. This contradicts the approach of this project making role assignments managed in the external system. As such it is necessary to disable assignments caching in Keystone ([role].caching = false). OpenFGASqlMultiplex:should_use_sql_backend method is cached (it is not