apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: restrict-route-backends
  annotations:
    policies.kyverno.io/title: Restrict HTTPRoute cross-namespace backends
    policies.kyverno.io/category: Gateway API
    policies.kyverno.io/severity: medium
    policies.kyverno.io/description: >-
      Keep backendRefs in the route namespace. Cross-namespace backends require
      ReferenceGrant and a reviewed exception path.
spec:
  validationFailureAction: Audit
  background: true
  rules:
    - name: deny-cross-namespace-backendrefs
      match:
        any:
          - resources:
              kinds:
                - HTTPRoute
      validate:
        message: >-
          HTTPRoute backendRefs must not set a different namespace than the
          route. Use same-namespace Services only.
        foreach:
          - list: "request.object.spec.rules[].backendRefs[]"
            preconditions:
              all:
                - key: "{{ element.namespace || '' }}"
                  operator: NotEquals
                  value: ""
            deny:
              conditions:
                any:
                  - key: "{{ element.namespace }}"
                    operator: NotEquals
                    value: "{{ request.namespace }}"