CNF-22870: Define constants for magic strings in istiocsr

Replace magic string literals with named constants:
- "Kubernetes" default cluster ID → defaultClusterID
- "default" Istio revision name → defaultIstioRevision
- Consolidate duplicate istiodCertificateDefaultDNSName constant
  into istiodCertificateCommonNameFmt (both were "istiod.%s.svc")

This improves readability and keeps test assertions in sync with
production defaults.

Author: sebrandon1

pkg/controller/istiocsr/certificates.go

@@ -87,8 +87,8 @@ func updateCertificateParams(istiocsr *v1alpha1.IstioCSR, certificate *certmanag
 		if revision == "" {
 			continue
 		}
-		if revision == "default" {
-			name := fmt.Sprintf(istiodCertificateDefaultDNSName, istiocsr.Spec.IstioCSRConfig.Istio.Namespace)
+		if revision == defaultIstioRevision {
+			name := fmt.Sprintf(istiodCertificateCommonNameFmt, istiocsr.Spec.IstioCSRConfig.Istio.Namespace)
 			dnsNames = append(dnsNames, name)
 			continue
 		}

pkg/controller/istiocsr/constants.go

@@ -45,15 +45,22 @@ const (
 	// containing the image version of the istiocsr as value.
 	istiocsrImageVersionEnvVarName = "ISTIOCSR_OPERAND_IMAGE_VERSION"
 
+	// defaultClusterID is the default Kubernetes cluster identifier used by istio-csr
+	// when no custom cluster ID is configured.
+	defaultClusterID = "Kubernetes"
+
+	// defaultIstioRevision is the Istio default revision name. When this revision is
+	// specified, the DNS SAN uses the base istiod service name rather than a
+	// revision-prefixed name.
+	defaultIstioRevision = "default"
+
 	// istiocsrGRPCEndpointFmt is the format string for the istiocsr GRPC service endpoint.
 	istiocsrGRPCEndpointFmt = "%s.%s.svc:%d"
 
-	// istiodCertificateCommonNameFmt is the format string for deriving the istiod certificate common name.
+	// istiodCertificateCommonNameFmt is the format string for deriving the istiod certificate common name
+	// and default DNS name.
 	istiodCertificateCommonNameFmt = "istiod.%s.svc"
 
-	// istiodCertificateDefaultDNSName is the format string for deriving the istiod certificate default DNS name.
-	istiodCertificateDefaultDNSName = "istiod.%s.svc"
-
 	// istiodCertificateRevisionBasedDNSName is the format string for deriving the istiod certificate DNS name
 	// for each defined revision.
 	istiodCertificateRevisionBasedDNSName = "istiod-%s.%s.svc"

pkg/controller/istiocsr/deployments.go

@@ -137,7 +137,7 @@ func updatePodTemplateLabels(deployment *appsv1.Deployment, resourceLabels map[s
 func updateArgList(deployment *appsv1.Deployment, istiocsr *v1alpha1.IstioCSR) {
 	istiocsrConfigs := istiocsr.Spec.IstioCSRConfig
 	// Default clusterID to "Kubernetes" if not provided.
-	clusterID := "Kubernetes"
+	clusterID := defaultClusterID
 	if istiocsrConfigs.Server != nil && istiocsrConfigs.Server.ClusterID != "" {
 		clusterID = istiocsrConfigs.Server.ClusterID
 	}

pkg/controller/istiocsr/deployments_test.go

@@ -1105,7 +1105,7 @@ func TestUpdateArgList(t *testing.T) {
 				// Server config is nil, so clusterID should default
 			},
 			expectedArgs: map[string]string{
-				"cluster-id": "Kubernetes",
+				"cluster-id": defaultClusterID,
 			},
 		},
 		{
@@ -1116,7 +1116,7 @@ func TestUpdateArgList(t *testing.T) {
 				}
 			},
 			expectedArgs: map[string]string{
-				"cluster-id": "Kubernetes",
+				"cluster-id": defaultClusterID,
 			},
 		},
 		{