feat: add SOCKS5 proxy documentation

Goal of this commit is to document the usage of SOCKS5 proxies to reach
the Kubernetes API.

content/en/docs/tasks/extend-kubernetes/socks5-proxy-access-api.md

@@ -0,0 +1,117 @@
+---
+title: Use a SOCKS5 Proxy to Access the Kubernetes API
+content_type: task
+weight: 42
+min-kubernetes-server-version: v1.25.0
+---
+
+<!-- overview -->
+This page shows how to use SOCKS5 proxying to access the API of a remote Kubernetes cluster. This is useful when the cluster you want to access does not expose its API directly on the public internet.
+
+## {{% heading "prerequisites" %}}
+
+{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
+
+<!-- steps -->
+
+## Overview
+
+{{< note >}}
+This example tunnels traffic using SSH, with the SSH client and server acting as a SOCKS proxy. You can instead use any other kind of [SOCKS5](https://en.wikipedia.org/wiki/SOCKS#SOCKS5) proxy.
+{{</ note >}}
+
+The following diagram represents what we're going to achieve in this tutorial:
+
+* We've got a _client machine_ from where we're going to create requests to talk to the Kubernetes API
+* The Kubernetes server/API is hosted on a _remote server_.
+* We leverage SSH to create a secure SOCKS5 tunnel between the _local_ and the _remote server_ on top of which the HTTPS traffic between the client and the Kubernetes API will flow.
+
+{{< mermaid >}}
+graph LR;
+
+  subgraph local[Local client machine]
+  client([client])-- local <br> traffic .->  local_ssh[Local SSH <br> SOCKS5 proxy];
+  end
+  local_ssh[SSH <br>SOCKS5 <br> proxy]-- SSH Tunnel -->sshd
+
+  subgraph remote[Remote server]
+  sshd[SSH <br> server]-- local traffic -->service1;
+  end
+  client([client])-. proxied HTTPs traffic <br> going through the proxy .->service1[Kubernetes API];
+
+  classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
+  classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
+  classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
+  class ingress,service1,service2,pod1,pod2,pod3,pod4 k8s;
+  class client plain;
+  class cluster cluster;
+{{</ mermaid >}}
+
+## Using ssh to create a SOCKS5 proxy
+
+This command starts a SOCKS5 proxy between your _client machine_ and the _remote server_ where the Kubernetes API is listening:
+
+```shell
+ssh -D 8080 -q -N username@kubernetes-jump-box.example
+```
+
+* `-D 8080`: opens a SOCKS proxy on local port :8080.
+* `-q`: quiet mode. Causes most warning and diagnostic messages to be suppressed.
+* `-N`: Do not execute a remote command. Useful for just forwarding ports.
+* `username@kubernetes-jump-box.example`: the remote SSH server where the Kubernetes cluster is running.
+
+## Client configuration
+
+To explore the Kubernetes API you'll first need to instruct your clients to send their queries through the SOCKS5 proxy we created earlier:
+
+for command-line tools, set the `https_proxy` environment variable in your and pass it to commands that you run.
+
+```shell
+export https_proxy=socks5://localhost:8080
+```
+
+When you set the `https_proxy` variable, tool such as `curl` route HTTPS traffic through the proxy that you configured. For this to work, the tool must support SOCKS5 proxying.
+
+{{< note >}}
+In this example localhost will not be the localhost of the _client machine_ but the localhost of the _remote server_. It could also be replaced by a hostname that is known by the _remote server_ and hosted further in the remote infrastructure.
+{{</ note >}}
+
+```shell
+curl -k -v https://localhost/api
+```
+
+To use the official Kubernetes client `kubectl` with a proxy, set the `proxy-url` element for the relevant `cluster` entry within  your `~/.kube/config` file. For example:
+
+```yaml
+apiVersion: v1
+clusters:
+- cluster:
+    certificate-authority-data: LRMEMMW2 # shortened for readability 
+    server: https://localhost            # the "Kubernetes API" in the diagram above
+    proxy-url: socks5://localhost:8080   # the "SSH SOCKS5 proxy" in the diagram above
+  name: default
+contexts:
+- context:
+    cluster: default
+    user: default
+  name: default
+current-context: default
+kind: Config
+preferences: {}
+users:
+- name: default
+  user:
+    client-certificate-data: LS0tLS1CR== # shortened for readability
+    client-key-data: LS0tLS1CRUdJT=      # shortened for readability
+```
+
+If the tunnel is operating and you use `kubectl` with a context that uses this cluster, you can interact with your cluster through that proxy. For example:
+
+```shell
+kubectl get pods
+```
+
+```console
+NAMESPACE     NAME                                     READY   STATUS      RESTARTS   AGE
+kube-system   coredns-85cb69466-klwq8                  1/1     Running     0          5m46s
+```