feat: support writting kubeconfig to a stream

pkg/client/kubeconfig.go

@@ -207,18 +207,28 @@ func KubeconfigWriteToPath(ctx context.Context, kubeconfig *clientcmdapi.Config,
 		defer output.Close()
 	}
 
+	err = KubeconfigWriteToStream(ctx, kubeconfig, output)
+	if err != nil {
+		return fmt.Errorf("failed to write file '%s': %w", output.Name(), err)
+	}
+
+	l.Log().Debugf("Wrote kubeconfig to '%s'", output.Name())
+
+	return nil
+}
+
+// KubeconfigWriteToStream takes a kubeconfig and writes it to stream
+func KubeconfigWriteToStream(ctx context.Context, kubeconfig *clientcmdapi.Config, writer io.Writer) error {
 	kubeconfigBytes, err := clientcmd.Write(*kubeconfig)
 	if err != nil {
 		return fmt.Errorf("failed to write kubeconfig: %w", err)
 	}
 
-	_, err = output.Write(kubeconfigBytes)
+	_, err = writer.Write(kubeconfigBytes)
 	if err != nil {
-		return fmt.Errorf("failed to write file '%s': %w", output.Name(), err)
+		return fmt.Errorf("failed to write stream '%s'", err)
 	}
 
-	l.Log().Debugf("Wrote kubeconfig to '%s'", output.Name())
-
 	return nil
 }
 
@@ -230,7 +240,7 @@ func KubeconfigMerge(ctx context.Context, newKubeConfig *clientcmdapi.Config, ex
 	for k, v := range newKubeConfig.Clusters {
 		if _, ok := existingKubeConfig.Clusters[k]; ok {
 			if !overwriteConflicting {
-				return fmt.Errorf("Cluster '%s' already exists in target KubeConfig", k)
+				return fmt.Errorf("cluster '%s' already exists in target KubeConfig", k)
 			}
 		}
 		existingKubeConfig.Clusters[k] = v
@@ -247,7 +257,7 @@ func KubeconfigMerge(ctx context.Context, newKubeConfig *clientcmdapi.Config, ex
 
 	for k, v := range newKubeConfig.Contexts {
 		if _, ok := existingKubeConfig.Contexts[k]; ok && !overwriteConflicting {
-			return fmt.Errorf("Context '%s' already exists in target KubeConfig", k)
+			return fmt.Errorf("context '%s' already exists in target KubeConfig", k)
 		}
 		existingKubeConfig.Contexts[k] = v
 	}