func IsValidWildcardDomainInCert(s string) bool {
	if s == "*" {
		return false
	}
	parts := strings.Split(s, ".")
	if len(parts) < 3 {
		return false
	}
	first := parts[0]
	rest := strings.Join(parts[1:], ".")
	return first == "*" && validation.ValidateFQDN(rest) == nil
}
true:  *
true:  *.example.com
false: *.com
false: a*.example.com
false: a*b.example.com
package v1alpha1
import (
	"net/url"
	"regexp"
	"strings"
	"github.com/kalmhq/kalm/controller/validation"
	apimachineryvalidation "k8s.io/apimachinery/pkg/api/validation"
	v1validation "k8s.io/apimachinery/pkg/apis/meta/v1/validation"
	"k8s.io/apimachinery/pkg/util/validation/field"
	apimachineryval "k8s.io/apimachinery/pkg/util/validation"
)
func isValidURL(s string) bool {
	u, err := url.Parse(s)
	if err != nil || u.Scheme == "" || u.Host == "" {
		return false
	}
	return true
}