How to test Kubernetes validation webhook with curl?

I want to test a validating webhook with curl.

There is a port-forwarding to that service via kubectl.

I created capi-cluster.yaml.

But this fails:

curl --insecure -X POST -H "Content-Type: application/json" \
    --data-binary @capi-cluster.yaml \
    https://127.0.0.1:9443/validate-cluster-x-k8s-io-v1beta1-cluster

{"kind":"Cluster","apiVersion":"cluster.x-k8s.io/v1beta1","response":{"uid":"","allowed":false,"status":{"metadata":{},"message":"unknown operation \"\"","code":400}}}

What needs to be changed to get it working?

I found the answer:

I need to create a json file like this:

{
  "kind": "AdmissionReview",
  "apiVersion": "admission.k8s.io/v1",
  "request": {
    "uid": "test-uid",
    "kind": {
      "group": "",
      "version": "v1",
      "kind": "Pod"
    },
    "resource": {
      "group": "",
      "version": "v1",
      "resource": "pods"
    },
    "namespace": "default",
    "operation": "CREATE",
    "object": <RESOURCE_JSON>,
    "oldObject": null,
    "dryRun": false,
    "options": {
      "apiVersion": "meta.k8s.io/v1",
      "kind": "CreateOptions"
    }
  }
}

Then convert my yaml to json with yq -oj, and insert it in above snippet.

Then it works:

curl --insecure -X POST -H "Content-Type: application/json" \
    --data-binary @t.json 
    https://127.0.0.1:9443/validate-cluster-x-k8s-io-v1beta1-cluster

{"kind":"AdmissionReview","apiVersion":"admission.k8s.io/v1","response":{"uid":"test-uid","allowed":true,"status":{"metadata":{},"code":200}}}