Your LightDrive address book belongs to your account. It is not a public profile or a shared company directory.
CardDAV clients authenticate before they can read or change contacts. Use HTTPS, keep certificate checking enabled, and give each long-lived client its own LightDrive client password that includes Contacts. Create it under Settings → Security → App & device access, selecting only the services the app needs. Your main LightDrive password, Vault app passwords, and client passwords without Contacts access do not authenticate to CardDAV.
A contact can contain sensitive information such as home addresses, phone numbers, birthdays, and notes. Add only the information you need, protect every synchronized device with a screen lock, and review an app’s privacy practices before granting it contacts access.