[RFC-0010] Add multi-tenancy lockdown for decryption and kubeconfig

Adds two new controller flags to enforce ServiceAccount usage in
multi-tenant clusters where administrators need to lock down workload
identity access:

- --default-decryption-service-account
- --default-kubeconfig-service-account

These flags complement the existing --default-service-account flag to
provide complete multi-tenancy lockdown coverage for all three classes
of ServiceAccount fields in the Kustomization API.

Signed-off-by: cappyzawa <[email protected]>

Author: cappyzawa

go.mod

@@ -24,7 +24,7 @@ require (
 	github.com/fluxcd/pkg/apis/event v0.18.0
 	github.com/fluxcd/pkg/apis/kustomize v1.11.0
 	github.com/fluxcd/pkg/apis/meta v1.18.0
-	github.com/fluxcd/pkg/auth v0.23.0
+	github.com/fluxcd/pkg/auth v0.25.0
 	github.com/fluxcd/pkg/cache v0.10.0
 	github.com/fluxcd/pkg/http/fetch v0.17.0
 	github.com/fluxcd/pkg/kustomize v1.19.0

go.sum

@@ -199,8 +199,8 @@ github.com/fluxcd/pkg/apis/kustomize v1.11.0 h1:0IzDgxZkc4v+5SDNCvgZhfwfkdkQLPXC
 github.com/fluxcd/pkg/apis/kustomize v1.11.0/go.mod h1:j302mJGDww8cn9qvMsRQ0LJ1HPAPs/IlX7CSsoJV7BI=
 github.com/fluxcd/pkg/apis/meta v1.18.0 h1:ACHrMIjlcioE9GKS7NGk62KX4NshqNewr8sBwMcXABs=
 github.com/fluxcd/pkg/apis/meta v1.18.0/go.mod h1:97l3hTwBpJbXBY+wetNbqrUsvES8B1jGioKcBUxmqd8=
-github.com/fluxcd/pkg/auth v0.23.0 h1:Xt89QO1Hzh7X0JFwCeONyxMlgOX/zOPx0eyIyFoKyF0=
-github.com/fluxcd/pkg/auth v0.23.0/go.mod h1:YEAHpBFuW5oLlH9ekuJaQdnJ2Q3A7Ny8kha3WY7QMnY=
+github.com/fluxcd/pkg/auth v0.25.0 h1:q8iJ9vdADiJxNA7EKNgEbIXNGbgqqTz6u975ziI3omk=
+github.com/fluxcd/pkg/auth v0.25.0/go.mod h1:YEAHpBFuW5oLlH9ekuJaQdnJ2Q3A7Ny8kha3WY7QMnY=
 github.com/fluxcd/pkg/cache v0.10.0 h1:M+OGDM4da1cnz7q+sZSBtkBJHpiJsLnKVmR9OdMWxEY=
 github.com/fluxcd/pkg/cache v0.10.0/go.mod h1:pPXRzQUDQagsCniuOolqVhnAkbNgYOg8d2cTliPs7ME=
 github.com/fluxcd/pkg/envsubst v1.4.0 h1:pYsb6wrmXOSfHXuXQHaaBBMt3LumhgCb8SMdBNAwV/U=

internal/controller/kustomization_configuration_error_test.go

@@ -178,7 +178,7 @@ data: {}
 	t.Run("object level workload identity feature gate enabled", func(t *testing.T) {
 		g := NewWithT(t)
 
-		t.Setenv(auth.EnvVarEnableObjectLevelWorkloadIdentity, "true")
+		t.Setenv(auth.EnvEnableObjectLevelWorkloadIdentity, "true")
 
 		kustomizationKey := types.NamespacedName{
 			Name:      fmt.Sprintf("invalid-config-%s", randStringRunes(5)),

internal/decryptor/decryptor.go

@@ -318,12 +318,10 @@ func (d *Decryptor) SetAuthOptions(ctx context.Context) {
 	case DecryptionProviderSOPS:
 		var opts []auth.Option
 
+		opts = append(opts, auth.WithClient(d.client))
+		opts = append(opts, auth.WithServiceAccountNamespace(d.kustomization.GetNamespace()))
 		if d.kustomization.Spec.Decryption.ServiceAccountName != "" {
-			serviceAccount := types.NamespacedName{
-				Name:      d.kustomization.Spec.Decryption.ServiceAccountName,
-				Namespace: d.kustomization.GetNamespace(),
-			}
-			opts = append(opts, auth.WithServiceAccount(serviceAccount, d.client))
+			opts = append(opts, auth.WithServiceAccountName(d.kustomization.Spec.Decryption.ServiceAccountName))
 		}
 
 		involvedObject := cache.InvolvedObject{

main.go

@@ -80,27 +80,29 @@ func main() {
 	)
 
 	var (
-		metricsAddr             string
-		eventsAddr              string
-		healthAddr              string
-		concurrent              int
-		concurrentSSA           int
-		requeueDependency       time.Duration
-		clientOptions           runtimeClient.Options
-		kubeConfigOpts          runtimeClient.KubeConfigOptions
-		logOptions              logger.Options
-		leaderElectionOptions   leaderelection.Options
-		rateLimiterOptions      runtimeCtrl.RateLimiterOptions
-		watchOptions            runtimeCtrl.WatchOptions
-		intervalJitterOptions   jitter.IntervalOptions
-		aclOptions              acl.Options
-		noRemoteBases           bool
-		httpRetry               int
-		defaultServiceAccount   string
-		sopsAgeSecret           string
-		featureGates            feathelper.FeatureGates
-		disallowedFieldManagers []string
-		tokenCacheOptions       pkgcache.TokenFlags
+		metricsAddr                     string
+		eventsAddr                      string
+		healthAddr                      string
+		concurrent                      int
+		concurrentSSA                   int
+		requeueDependency               time.Duration
+		clientOptions                   runtimeClient.Options
+		kubeConfigOpts                  runtimeClient.KubeConfigOptions
+		logOptions                      logger.Options
+		leaderElectionOptions           leaderelection.Options
+		rateLimiterOptions              runtimeCtrl.RateLimiterOptions
+		watchOptions                    runtimeCtrl.WatchOptions
+		intervalJitterOptions           jitter.IntervalOptions
+		aclOptions                      acl.Options
+		noRemoteBases                   bool
+		httpRetry                       int
+		defaultServiceAccount           string
+		defaultDecryptionServiceAccount string
+		defaultKubeConfigServiceAccount string
+		sopsAgeSecret                   string
+		featureGates                    feathelper.FeatureGates
+		disallowedFieldManagers         []string
+		tokenCacheOptions               pkgcache.TokenFlags
 	)
 
 	flag.StringVar(&metricsAddr, "metrics-addr", ":8080", "The address the metric endpoint binds to.")
@@ -112,7 +114,9 @@ func main() {
 	flag.BoolVar(&noRemoteBases, "no-remote-bases", false,
 		"Disallow remote bases usage in Kustomize overlays. When this flag is enabled, all resources must refer to local files included in the source artifact.")
 	flag.IntVar(&httpRetry, "http-retry", 9, "The maximum number of retries when failing to fetch artifacts over HTTP.")
-	flag.StringVar(&defaultServiceAccount, "default-service-account", "", "Default service account used for impersonation.")
+	flag.StringVar(&defaultServiceAccount, auth.ControllerFlagDefaultServiceAccount, "", "Default service account used for impersonation.")
+	flag.StringVar(&defaultDecryptionServiceAccount, auth.ControllerFlagDefaultDecryptionServiceAccount, "", "Default service account used for decryption.")
+	flag.StringVar(&defaultKubeConfigServiceAccount, auth.ControllerFlagDefaultKubeConfigServiceAccount, "", "Default service account used for kubeconfig.")
 	flag.StringVar(&sopsAgeSecret, "sops-age-secret", "", "The name of a Kubernetes secret in the RUNTIME_NAMESPACE containing a SOPS age decryption key for fallback usage.")
 	flag.StringArrayVar(&disallowedFieldManagers, "override-manager", []string{}, "Field manager disallowed to perform changes on managed resources.")
 
@@ -146,6 +150,15 @@ func main() {
 		auth.EnableObjectLevelWorkloadIdentity()
 	}
 
+	// NOTE: defaultServiceAccount is used for regular impersonation, not workload identity lockdown
+
+	if defaultDecryptionServiceAccount != "" {
+		auth.SetDefaultDecryptionServiceAccount(defaultDecryptionServiceAccount)
+	}
+	if defaultKubeConfigServiceAccount != "" {
+		auth.SetDefaultKubeConfigServiceAccount(defaultKubeConfigServiceAccount)
+	}
+
 	if err := intervalJitterOptions.SetGlobalJitter(nil); err != nil {
 		setupLog.Error(err, "unable to set global jitter")
 		os.Exit(1)