I have written an app that lets users download detailed grade reports from an assignment that uses a rubric. Now I'm struggling to figure out how best to let users access it. I have already installed it as an account navigation tool, and that works fine, but people have to contact an admin to get their data. I can install it in a course as a course nav, and require each user to provide an instructor-level access token, but that's not really the right place for it, since it is built to allow you to export data from any course you own, not just the one containing the link. Also, LTI course nav links that are set to be visible only to admins don't appear gray, which I'm afraid will make faculty nervous about students seeing the link.
So, now I'm trying the user navigation extension, which I've never used before, and I'm having trouble installing it. Ideally I'd like users to be able to install this themselves, since the vast majority of our users don't need it. I tried installing via a course settings apps tab, but that didn't work, and even if it had, it feels wrong. What is the recommended way to install this sort of external tool? Must I do it at the level of an account or sub account? If so, what determines which users get the link?