support context concatenation for self contained wc client certificat…

…es (#853)

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project's packages adheres to [Semantic Versioning](http://semver.org/s
 
 ## [Unreleased]
 
+### Added
+
+- In the `login` command, allow concatenation of contexts in destination file when creating WC client certificates with `--self-contained` flag.
+
 ## [2.17.0] - 2022-07-07
 
 ### Added

cmd/login/clientcert.go

@@ -19,6 +19,7 @@ import (
 	"github.com/giantswarm/backoff"
 	"github.com/giantswarm/k8smetadata/pkg/label"
 	"github.com/giantswarm/microerror"
+	"github.com/imdario/mergo"
 	"github.com/spf13/afero"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -354,11 +355,22 @@ func printWCClientCertCredentials(k8sConfigAccess clientcmd.ConfigAccess, fs afe
 		},
 		CurrentContext: contextName,
 	}
-	if exists, err := afero.Exists(fs, c.filePath); exists {
-		return "", false, microerror.Maskf(fileExistsError, "The destination file %s already exists. Please specify a different destination.", c.filePath)
-	} else if err != nil {
+	// If the destination file exists, we merge the contexts contained in it with the newly created one
+	exists, err := afero.Exists(fs, c.filePath)
+	if err != nil {
 		return "", false, microerror.Mask(err)
 	}
+	if exists {
+		existingKubeConfig, err := clientcmd.LoadFromFile(c.filePath)
+		if err != nil {
+			return "", false, microerror.Mask(err)
+		}
+		err = mergo.Merge(&kubeconfig, existingKubeConfig, mergo.WithOverride)
+		if err != nil {
+			return "", false, microerror.Mask(err)
+		}
+		kubeconfig.CurrentContext = contextName
+	}
 	err = clientcmd.WriteToFile(kubeconfig, c.filePath)
 	if err != nil {
 		return "", false, microerror.Mask(err)

go.mod

@@ -20,6 +20,7 @@ require (
 	github.com/giantswarm/micrologger v0.6.0
 	github.com/giantswarm/release-operator/v3 v3.2.0
 	github.com/google/go-cmp v0.5.8
+	github.com/imdario/mergo v0.3.12
 	github.com/pkg/errors v0.9.1
 	github.com/rhysd/go-github-selfupdate v1.2.3
 	github.com/skratchdot/open-golang v0.0.0-20200116055534-eef842397966
@@ -79,7 +80,6 @@ require (
 	github.com/google/uuid v1.3.0 // indirect
 	github.com/googleapis/gnostic v0.5.5 // indirect
 	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79 // indirect
-	github.com/imdario/mergo v0.3.12 // indirect
 	github.com/inconshreveable/go-update v0.0.0-20160112193335-8152e7eb6ccf // indirect
 	github.com/inconshreveable/mousetrap v1.0.0 // indirect
 	github.com/josharian/intern v1.0.0 // indirect