fix: properly format IPv6 addresses in server URLs

When provisioning nodes with IPv6 control plane endpoints, the bootstrap
provider was generating invalid server URLs in the RKE2 configuration.

Invalid format:  https://fd12:3456:890b::250:6443
Correct format:  https://[fd12:3456:890b::250]:6443

This fix uses the standard library net.JoinHostPort function which
properly handles IPv6 bracket notation per RFC 3986. The function
automatically wraps IPv6 addresses in brackets while leaving IPv4
addresses and hostnames unchanged.

The fix is applied to all three server URL generation points:
- Init control plane config
- Join control plane config
- Worker node config

This eliminates the need for sed workarounds in user manifests.

Fixes: Invalid IPv6 URL parsing in RKE2 bootstrap config
Signed-off-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Kristian-ZH

bootstrap/internal/controllers/rke2config_controller.go

@@ -22,6 +22,8 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
+	"strconv"
 	"time"
 
 	"github.com/go-logr/logr"
@@ -62,7 +64,6 @@ import (
 const (
 	filePermissions  string = "0640"
 	registrationPort int    = 9345
-	serverURLFormat  string = "https://%v:%v"
 	tokenPrefix      string = "-token"
 )
 
@@ -469,7 +470,7 @@ func (r *RKE2ConfigReconciler) handleClusterNotInitialized(ctx context.Context,
 			Cluster:              *scope.Cluster,
 			ControlPlaneEndpoint: scope.Cluster.Spec.ControlPlaneEndpoint.Host,
 			Token:                token,
-			ServerURL:            fmt.Sprintf(serverURLFormat, registrationAddress, registrationPort),
+			ServerURL:            fmt.Sprintf("https://%s", net.JoinHostPort(registrationAddress, strconv.Itoa(registrationPort))),
 			ServerConfig:         scope.ControlPlane.Spec.ServerConfig,
 			AgentConfig:          scope.Config.Spec.AgentConfig,
 			Ctx:                  ctx,
@@ -713,7 +714,7 @@ func (r *RKE2ConfigReconciler) joinControlplane(ctx context.Context, scope *Scop
 			Cluster:              *scope.Cluster,
 			Token:                token,
 			ControlPlaneEndpoint: scope.Cluster.Spec.ControlPlaneEndpoint.Host,
-			ServerURL:            fmt.Sprintf(serverURLFormat, scope.ControlPlane.Status.AvailableServerIPs[0], registrationPort),
+			ServerURL:            fmt.Sprintf("https://%s", net.JoinHostPort(scope.ControlPlane.Status.AvailableServerIPs[0], strconv.Itoa(registrationPort))),
 			ServerConfig:         scope.ControlPlane.Spec.ServerConfig,
 			AgentConfig:          scope.Config.Spec.AgentConfig,
 			Ctx:                  ctx,
@@ -863,7 +864,7 @@ func (r *RKE2ConfigReconciler) joinWorker(ctx context.Context, scope *Scope) (re
 
 	configStruct, configFiles, err := rke2.GenerateWorkerConfig(
 		rke2.AgentConfigOpts{
-			ServerURL:              fmt.Sprintf(serverURLFormat, scope.ControlPlane.Status.AvailableServerIPs[0], registrationPort),
+			ServerURL:              fmt.Sprintf("https://%s", net.JoinHostPort(scope.ControlPlane.Status.AvailableServerIPs[0], strconv.Itoa(registrationPort))),
 			Token:                  token,
 			AgentConfig:            scope.Config.Spec.AgentConfig,
 			Ctx:                    ctx,