Restrict Ingress Classes

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: restrict-ingress-classes
  annotations:
    policies.kyverno.io/title: Restrict Ingress Classes
    policies.kyverno.io/category: Sample
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: Ingress
    policies.kyverno.io/minversion: 1.6.0
    policies.kyverno.io/description: Ingress classes should only be allowed which match up to deployed Ingress controllers in the cluster. Allowing users to define classes which cannot be satisfied by a deployed Ingress controller can result in either no or undesired functionality. This policy checks Ingress resources and only allows those which define `HAProxy` or `nginx` in the respective annotation. This annotation has largely been replaced as of Kubernetes 1.18 with the IngressClass resource.
spec:
  validationFailureAction: Audit
  background: true
  rules:
    - name: validate-ingress
      match:
        any:
          - resources:
              kinds:
                - Ingress
      validate:
        message: Unknown ingress class.
        pattern:
          metadata:
            annotations:
              kubernetes.io/ingress.class: HAProxy | nginx