Hi @Isak_Hejnesen welcome to the forum!
You have a few options.
Most of them are not as direct as you were hoping for, unfortunately, but they will indeed work.
1 Password - Entire Site
You can set 1 password for the entire site natively within Webflow. Give the same password out to everyone and they have full access to every page. Not ideal.
1 Password - Per Page
You can set each static page natively within Webflow to have a unique password. Again, not ideal since you’d have to create a static page per customer for those downloads. But if your client doesn’t have a lot of customers, this could work.
As you’ve found out, restricted access is at the CMS Collection level. But you have a couple of creative options.
Each item within a collection has a slug. You get to control the slug name. The slug is how you navigate with the web browser to that specific item in your collection. The pattern is…
So you could think of
slug as the customer name.
What people often do is replace that
slug with a long auto-generated jumble of characters that is not easily guessable.
…and make sure nothing is referenced if you auto-generate a sitemap.
With all of this gated behind Memberships, random folks can’t ever try to guess that url, and only your clients existing customers would have the ability to do so. But it’s highly unlikely they would.
Also, this can all be automated.
If your client does not have a lot of customers, then you can get around this by creating 1 CMS Collection per customer.
Again, not ideal, but you then get the control you’re looking for.
If you’d like an overview, here is a tutorial walking through a Webflow Memberships build, it may give you a few ideas:
You could put aside all of the options above and go with a third party solution. This is the one I’ve used a lot and it will exactly meet your needs.
Here are some screencasts walking through various setups that’ll work with what you’ve asked for:
Hope that helps!