code: func ValidateCertSANs(altnames []string, fldPath *field.Path) field.ErrorList {
  	allErrs := field.ErrorList{}
  	for _, altname := range altnames {
  		if errs := validation.IsDNS1123Subdomain(altname); len(errs) != 0 {
  			if errs2 := validation.IsWildcardDNS1123Subdomain(altname); len(errs2) != 0 {
  				if net.ParseIP(altname) == nil {
  					allErrs = append(allErrs, field.Invalid(fldPath, altname, fmt.Sprintf("altname is not a valid IP address, DNS label or a DNS label with subdomain wildcards: %s; %s", strings.Join(errs, "; "), strings.Join(errs2, "; "))))
  				}
  			}
  		}
  	}
  	return allErrs
  }
docs: // ValidateCertSANs validates alternative names