Vault documentation: added new code sample to Kubernetes documentation (#12774)

* added new code sample for k8s auth

* Update kubernetes.mdx

removed spacing

website/content/docs/auth/kubernetes.mdx

@@ -176,3 +176,86 @@ The Kubernetes Auth Plugin has a full HTTP API. Please see the
 [API docs](/api/auth/kubernetes) for more details.
 
 [k8s-tokenreview]: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.19/#tokenreview-v1beta1-authentication-k8s-io
+
+## Code Example
+
+The following code snippet demonstrates the Kubernetes auth method to authenticate
+with Vault.
+
+<CodeTabs heading="kubernetes auth example">
+
+<CodeBlockConfig lineNumbers>
+
+```go
+package main
+
+import (
+	"fmt"
+	"os"
+
+	vault "github.com/hashicorp/vault/api"
+)
+
+// Fetches a key-value secret (kv-v2) after authenticating to Vault with a Kubernetes service account.
+//
+// As the client, all we need to do is pass along the JWT token representing our application's Kubernetes Service Account in our login request to Vault.
+//
+// For a more in-depth setup explanation, please see the full version of this code in the hashicorp/vault-examples repo.
+func getSecretWithKubernetesAuth() (string, error) {
+	// If set, the VAULT_ADDR environment variable will be the address that your pod uses to communicate with Vault.
+	config := vault.DefaultConfig() // modify for more granular configuration
+
+	client, err := vault.NewClient(config)
+	if err != nil {
+		return "", fmt.Errorf("unable to initialize Vault client: %w", err)
+	}
+
+	// Read the service-account token from the path where the token's Kubernetes Secret is mounted.
+	// By default, Kubernetes will mount this to /var/run/secrets/kubernetes.io/serviceaccount/token
+	// but an administrator may have configured it to be mounted elsewhere.
+	jwt, err := os.ReadFile("path/to/service-account-token")
+	if err != nil {
+		return "", fmt.Errorf("unable to read file containing service account token: %w", err)
+	}
+
+	params := map[string]interface{}{
+		"jwt":  string(jwt),
+		"role": "dev-role-k8s", // the name of the role in Vault that was created with this app's Kubernetes service account bound to it
+	}
+
+	// log in to Vault's Kubernetes auth method
+	resp, err := client.Logical().Write("auth/kubernetes/login", params)
+	if err != nil {
+		return "", fmt.Errorf("unable to log in with Kubernetes auth: %w", err)
+	}
+	if resp == nil || resp.Auth == nil || resp.Auth.ClientToken == "" {
+		return "", fmt.Errorf("login response did not return client token")
+	}
+
+	// now you will use the resulting Vault token for making all future calls to Vault
+	client.SetToken(resp.Auth.ClientToken)
+
+	// get secret from Vault
+	secret, err := client.Logical().Read("kv-v2/data/creds")
+	if err != nil {
+		return "", fmt.Errorf("unable to read secret: %w", err)
+	}
+
+	data, ok := secret.Data["data"].(map[string]interface{})
+	if !ok {
+		return "", fmt.Errorf("data type assertion failed: %T %#v", secret.Data["data"], secret.Data["data"])
+	}
+
+	// data map can contain more than one key-value pair, in this case we're just grabbing one of them
+	key := "password"
+	value, ok := data[key].(string)
+	if !ok {
+		return "", fmt.Errorf("value type assertion failed: %T %#v", data[key], data[key])
+	}
+
+	return value, nil
+}
+```
+</CodeBlockConfig>
+
+</CodeTabs>