Fix in-cluster API discovery documentation (kubernetes#36691)

* Fix in-cluster API discovery documentation

The documentation incorrectly describes the way that client libraries
discover the Kubernetes API server. While the `kubernetes.default.svc`
DNS is provided as a convenience, **all** of the officially supported API
clients use environment variables to discover the address of the API server.

This change updates the documentation to reflect this.

Signed-off-by: Oliver Gould <[email protected]>

* Review feedback

* Fixup

Signed-off-by: Oliver Gould <[email protected]>

content/en/docs/tasks/run-application/access-api-from-pod.md

@@ -42,10 +42,18 @@ securely with the API server.
 
 ### Directly accessing the REST API
 
-While running in a Pod, the Kubernetes apiserver is accessible via a Service named
-`kubernetes` in the `default` namespace. Therefore, Pods can use the
-`kubernetes.default.svc` hostname to query the API server. Official client libraries
-do this automatically.
+While running in a Pod, your container can create an HTTPS URL for the Kubernetes API
+server by fetching the `KUBERNETES_SERVICE_HOST` and `KUBERNETES_SERVICE_PORT_HTTPS`
+environment variables. The API server's in-cluster address is also published to a
+Service named `kubernetes` in the `default` namespace so that pods may reference
+`kubernetes.default.svc` as a DNS name for the local API server.
+
+{{< note >}}
+Kubernetes does not guarantee that the API server has a valid certificate for
+the hostname  `kubernetes.default.svc`;
+however, the control plane **is** expected to present a valid certificate for the
+hostname or IP address that `$KUBERNETES_SERVICE_HOST` represents.
+{{< /note >}}
 
 The recommended way to authenticate to the API server is with a
 [service account](/docs/tasks/configure-pod-container/configure-service-account/)