Download/files management software for clients for website

I've got different versions of a software that I'd like to distribute to clients (B2B). For example, one might be the base version, an extended version, and a trial version. These would be separate zip files. They are versioned as well.

These files are made available to clients either for trial or after they sign up for a license, and different licenses would give them access to different variants of the "software" (it's not exactly a software, it's just a file, but it doesn't matter for the sake of this question).

Putting these files on a webserver and allow password-protected HTTP access is not ideal as it doesn't allow a fine-grained enough permission model, e.g. for example I may want to give one client access to an update or a beta version, and not to another, and I'd end up creating a separate folder for each client for each version, which is very messy and means duplication a lot of files.

I guess what I am looking for is some simple, web-based "download portal" software, where I can create a web account for each customer. Ideally this would support the concept of "release channels" or something like that, and I could then assign each customer to a release channel, and to specific files in addition to that, to steer which customer has access to which files. I am using a self-hosted WordPress for the main website so I was thinking it would be great to have such a portal on a sub-domain like download.company.com and it ideally would use the WordPress authentication mechanism.

I don't want to program such a software myself though and I also didn't find an existing WP plugin that would do something like that. I am mentioning WP but this is not a WP-question, I am looking for any (good) solution - if it was able to use the WP-authentication mechanism, it would just be a really useful feature.

Does any solution like this exist? How would I best go about it? It seems that any B2B company distributing files and/or software to customers would have this problem. Do they all develop their own solution?

I wasn't 100% sure whether this fits on the StackOverflow, SuperUser, WebApps or Webmasters sites, if it's not appropriate here, I am happy to be directed to the most appropriate place.