basehub: reduce hub.loadRoles and clarify the situation

Author: consideRatio

helm-charts/basehub/values.yaml

@@ -590,15 +590,37 @@ jupyterhub:
                 matchLabels:
                   app.kubernetes.io/component: traefik
   hub:
-    loadRoles:
-      # Should use this, not hub.config.JupyterHub.load_roles - that will
-      # override any existing load_roles set by z2jh
-      service-use:
-        name: user
-        scopes:
-          # Allow all users access to 'services', which includes dask-gateway & configurator
-          - access:services
-          - self
+    # hub.loadRoles is z2jh native config to enable configuration of
+    # c.JupyterHub.load_roles without overriding a list - use it instead of the
+    # passthrough config hub.config.JupyterHub.load_roles.
+    #
+    # - About jupyterhub-configurator service access
+    #
+    #   The JupyterHub admin users get the scope access:services by being
+    #   admins, which includes the scope access:services!service=configurator.
+    #   This makes them not need additional scope requests to work with
+    #   jupyterhub-configurator that also require users to be admins anyhow.
+    #
+    #   ref: https://github.com/yuvipanda/jupyterhub-configurator/blob/f46fb4e81b1de74c4fcaa5a7763fb230265bab90/jupyterhub_configurator/app.py#L100-L109
+    #
+    # - About dask-gateway service access
+    #
+    #   Providing access:services!service=dask-gateway has no effect, as
+    #   dask-gateway the client passes the jupyterhub user's jupyterhub api
+    #   token to the dask-gateway-server, which then just verifies that the api
+    #   token is associated with an actual user using the api token itself. Due
+    #   to that, we can't limit access to dask-gateway by providing that scope
+    #   only to some users.
+    #
+    #   Considerations of updating dask-gateway to gate access via
+    #   access:services!service=dask-gateway is considered in the linked issue.
+    #
+    #   ref: https://github.com/dask/dask-gateway/issues/829
+    #
+    # loadRoles ref (z2jh): https://z2jh.jupyter.org/en/stable/resources/reference.html#hub-loadroles
+    # load_roles ref (jh):  https://jupyterhub.readthedocs.io/en/stable/rbac/roles.html#defining-roles
+    #
+    loadRoles: {}
     config:
       JupyterHub:
         # Allow unauthenticated prometheus requests