Keycloak JS Policy $evaluation is Undefined - keycloak

Question

I am creating a JS custom policy for keycloak following the guide:
https://www.keycloak.org/docs/latest/authorization_services/index.html#_policy_js
Unfortunately in my script all variables are undefined for some reaseon.
js
var context = $evaluation.context;
var identity = context.identity;
var permission = $evaluation.permission;
var resource = permission.resource;
var attributes = identity.getAttributes();
print('**** evaluation ' + JSON.stringify($evaluation));
print('**** context ' + JSON.stringify(context));
print('**** identity ' + JSON.stringify(identity));
print('**** attributes ' + JSON.stringify(attributes));
if (attributes.owner == identity.id) {
$evaluation.grant();
}
Keycloak logs:
keycloak-authorization-keycloak-1 | 2022-12-30 14:52:46,319 WARN [org.keycloak.connections.httpclient.DefaultHttpClientFactory] (executor-thread-2) TruststoreProvider is disabled
keycloak-authorization-keycloak-1 | 2022-12-30 14:52:48,087 WARN [org.keycloak.services.managers.AuthenticationManager] (executor-thread-1) Required action provider factory 'CONFIGURE_RECOVERY_AUTHN_CODES' configured in the realm 'myrealm' is not available. Provider not found or feature is disabled.
keycloak-authorization-keycloak-1 | 2022-12-30 14:52:48,088 WARN [org.keycloak.services.managers.AuthenticationManager] (executor-thread-1) Required action provider factory 'UPDATE_EMAIL' configured in the realm 'myrealm' is not available. Provider not found or feature is disabled.
keycloak-authorization-keycloak-1 | **** evaluation undefined
keycloak-authorization-keycloak-1 | **** context undefined
keycloak-authorization-keycloak-1 | **** identity undefined
keycloak-authorization-keycloak-1 | **** attributes undefined
services:
keycloak:
image: quay.io/keycloak/keycloak:latest
volumes:
- keycloak:/opt/keycloak/data
- ./js-policies/target/js-policies.jar:/opt/keycloak/providers/js-policies.jar
ports:
- 9000:8080
environment:
KEYCLOAK_ADMIN: admin
KEYCLOAK_ADMIN_PASSWORD: admin
command:
- start-dev

Answer 1

It turns out the evaluation context is not null - it was JSON.stringify that was returning null for some reason.
I suppose it is due to a limitation of the Java Nashorn Engine.
If you are curious - the $evaluation gets mapped to the class DefaultEvaluation. From there on you can deduce all possible proeprties and values you can use in your policy by consulting the javadoc in the bellow link.
https://www.keycloak.org/docs-api/18.0/javadocs/org/keycloak/authorization/policy/evaluation/DefaultEvaluation.html