Add deprecation warning info

content/en/docs/reference/access-authn-authz/extensible-admission-controllers.md

@@ -628,6 +628,47 @@ So a webhook response to add that label would be:
 {{% /tab %}}
 {{< /tabs >}}
 
+Starting in v1.19, admission webhooks can optionally return warning messages that are returned to the requesting client.
+Warnings can be sent with allowed or rejected admission responses.
+No "Warning:" prefix should be included in the message.
+Warning messages should describe a problem the client making the API request should correct or be aware of.
+Limit warnings to 120 characters if possible. Warnings over 256 characters and large numbers of warnings may be truncated.
+
+{{< tabs name="AdmissionReview_response_warning" >}}
+{{% tab name="admission.k8s.io/v1" %}}
+```json
+{
+  "apiVersion": "admission.k8s.io/v1",
+  "kind": "AdmissionReview",
+  "response": {
+    "uid": "<value from request.uid>",
+    "allowed": true,
+    "warnings": [
+      "duplicate envvar entries specified with name MY_ENV",
+      "memory request less than 4MB specified for container mycontainer, which will not start successfully"
+    ]
+  }
+}
+```
+{{% /tab %}}
+{{% tab name="admission.k8s.io/v1beta1" %}}
+```json
+{
+  "apiVersion": "admission.k8s.io/v1beta1",
+  "kind": "AdmissionReview",
+  "response": {
+    "uid": "<value from request.uid>",
+    "allowed": true,
+    "warnings": [
+      "duplicate envvar entries specified with name MY_ENV",
+      "memory request less than 4MB specified for container mycontainer, which will not start successfully"
+    ]
+  }
+}
+```
+{{% /tab %}}
+{{< /tabs >}}
+
 ## Webhook configuration
 
 To register admission webhooks, create `MutatingWebhookConfiguration` or `ValidatingWebhookConfiguration` API objects.