template.yaml

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: k8srestricttype
spec:
  crd:
    spec:
      names:
        kind: K8sRestrictType
      validation:
        openAPIV3Schema:
          properties:
            namespace:
              type: string

  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8srestrictype

        violation[{ "msg": msg }] {
          object := input.review.object
          
          object.metadata.namespace == input.parameters.namespace
          
          msg := sprintf("%v is not allowed for creation in namespace %v", [input.review.kind.kind, input.parameters.namespace])
        }