Require array item using Kyverno policy

Trying to create a Kyverno policy that requires certain array values. They have examples for "maps" such as labels, but I didn't see anything specifically about arrays.

Here's a sample Application resource:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: authentication
  namespace: openshift-gitops
spec:
  destination:
    server: 'https://kubernetes.default.svc'
  project: cluster-config
  source:
    path: cluster-config/authentication
    repoURL: 'https://example.com/scm/gitops/openshift-prod-cluster.git'
    targetRevision: master
  syncPolicy:
    automated:
      selfHeal: true
    retry:
      backoff:
        duration: 15s
        factor: 2
        maxDuration: 5m
      limit: 15
    syncOptions:
      - ServerSideApply=true
      - Validate=false
      - FailOnSharedResource=true

This is my latest attempt, but both rules fail for every application:

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: require-server-side-sync
  annotations:
    policies.kyverno.io/title: Use Server-Side Sync
    policies.kyverno.io/category: Argo
    policies.kyverno.io/severity: low
    policies.kyverno.io/subject: Application
    kyverno.io/kyverno-version: 1.6.0
    policies.kyverno.io/minversion: 1.6.0
    kyverno.io/kubernetes-version: "1.23"
    policies.kyverno.io/description: >-
      By default, Argo CD executes `kubectl apply` operation to apply the configuration stored in Git. 
      This is a client side operation that relies on `kubectl.kubernetes.io/last-applied-configuration` annotation to 
      store the previous resource state. However, using server-side sync avoids issues with `kubectl.kubernetes.io/last-applied-configuration`
      growing so large that it breaks standard syncing, and allows patching of existing cluster resources that are not fully
      managed by Argo. Certain patch yamls may not be "valid" according to their resource definition and will need client-side
      validation to be disabled in order to work. (`kube-api` will still perform server-side validation of the patched resource before applying the change.)
spec:
  validationFailureAction: Audit
  background: true
  rules:
    - name: enable-server-side-sync
      match:
        any:
          - resources:
              kinds:
                - Application
      validate:
        message: >-
          Server-side sync option must be enabled.
        pattern:
          - spec:
              syncPolicy:
                ^(syncOptions):
                - ServerSideApply: true
    - name: disable-client-side-validation
      match:
        any:
          - resources:
              kinds:
                - Application
      validate:
        message: >-
          client-side validation must be disabled
        pattern:
          - spec:
              syncPolicy:
                syncOptions:
                  - Validate=false

so what's the best way to require an array value?

Unfortunately, the Existence anchor doesn't presently support an array of strings, only an array of objects. I've created an enhancement to get this added. For now, you can use a deny statement with a simple JMESPath expression to check that your strings are present.

apiVersion: kyverno.io/v2beta1
kind: ClusterPolicy
metadata:
  name: require-server-side-sync
spec:
  validationFailureAction: Enforce
  background: true
  rules:
    - name: enable-server-side-sync
      match:
        any:
          - resources:
              kinds:
                - Application
      validate:
        message: Server-side sync option must be enabled.
        deny:
          conditions:
            all:
            - key: ServerSideApply=true
              operator: AnyNotIn
              value: "{{ request.object.spec.syncPolicy.syncOptions[] }}"
    - name: disable-client-side-validation
      match:
        any:
          - resources:
              kinds:
                - Application
      validate:
        message: client-side validation must be disabled
        deny:
          conditions:
            all:
            - key: Validate=false
              operator: AnyNotIn
              value: "{{ request.object.spec.syncPolicy.syncOptions[] }}"