You can make a link private by enabling password protection for that link. Only people with the correct password will be redirected to the actual content. 

To do this,

1. Navigate to the detailed configuration of the link by click on the edit button

2. Click on the password modal

3. Click on Enable Password checkbox and enter a password. Click the Update button to save the changes.

Once password protection is configured, next time when users access the link, they'll be shown a page which expects a password to get redirected to the original url.