You can't protect a "link" as such; but you can protect the *folder* that
excel file is kept in. I assume you mean to protect a file or folder, such
as the excel file with the information you stated below.
Your host might provide a solution, depending on its operating system etc.
For example the hosting control panels like "CPanel" and "Helm" provide
features such as "protected folders". Whether or not your host has these
options enabled or whether they use Cpanel (Linux/Unix) or "Helm" (Windows)
or some other web-based control panel that allows their users to control
aspects of their hosting packages, is to to the host.