My preferred option is a quick-and-dirty, though very common, solution. The vendor has a “Support” page that contains limited “public” information. However the page includes a user “sign in” option so that authorised users can access all the “private” data that you have concerning your product.
This page can be accessed via the public website as well as via the software (such as “Help > On-line Support”).
You can be creative with the sign in details. The user name might be the licenced user name (which might be entered when the software is first installed). The password might be a code that is issued at the time of sale, but that is subject to a compulsory password change on first use, or even as part of a post-sales validation process. There are as many options for sign in details as one’s imagination can dream up.