TLSServerName is not taken into account

[nicolas-goudry]

Describe the bug

When using a kubeconfig which defines a tls-server-name field different from the server field, the client fails to validate the cluster certificate.

As a workaround, setting insecure-skip-tls-verify: true and removing certificate-authority-data from the kubeconfig file works.

Client Version

20

Kubernetes Version

1.28.6

Java Version

17

To Reproduce

Get a kubeconfig with a tls-server-name field different from the server field. This is the case with the kubeconfig files generated by Teleport. Run the KubeConfigFileClientExample.java:

cd examples/examples-release-20
mvn -X clean install exec:java -Dexec.mainClass="io.kubernetes.client.examples.KubeConfigFileClientExample"

Expected behavior

The client respects the tls-server-name field and uses this hostname to verify the TLS certificate.

KubeConfig

apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: REDACTED
    server: REDACTED
    tls-server-name: REDACTED
  name: REDACTED
contexts:
- context:
    cluster: REDACTED
    extensions:
    - extension: sandbox
      name: teleport.kube.name
    user: REDACTED
  name: REDACTED
current-context: REDACTED
kind: Config
preferences: {}
users:
- name: REDACTED
  user:
    exec:
      apiVersion: client.authentication.k8s.io/v1beta1
      args:
      - kube
      - credentials
      - --kube-cluster=sandbox
      - --teleport-cluster=REDACTED
      - --proxy=REDACTED
      command: tsh
      env: null
      provideClusterInfo: false

Server (please complete the following information):

• OS: Linux
• Environment: system
• Cloud: Azure/Teleport

Additional context

[brendandburns]

Yeah, that's not currently supported in our TLS. We'd be happy to take a PR to add support.

[nicolas-goudry]

Yeah, that's not currently supported in our TLS. We'd be happy to take a PR to add support.

I’m not a Java developer, I reported this issue because some applications from my company use the Java client and some of our customers use Teleport so the said apps don’t work for them.

Our Java developer don’t have any bandwidth to take this matter into his hands, so I hope someone could work on this 🙏

[arsenalzp]

Hello,
Can we consider this issue like one for newcomers in this project?