What is the actual problem thats being solved here? Is cache-sniffing being actively used for fingerprinting or something?
Whats going on here?
Want to know if your user has previously visited a specific website? Time how long it takes to load their CSS file, if it's instant then you know where they have been.
You can tell if they have an account on that site by timing the load of an asset that's usually only shown to logged-in users.
All of the browser manufacturers decided to make this change (most of them over 5 years ago now) for privacy reasons, even though it made their products worse in that they would be slower for their users.
In the days of webpack, not so much.
Most other CDNs similarly support tracking services.
As the article says the actual cost of partitioning is negligible, the cost of not partitioning is that nothing can prevent cross site tracking and invasion of privacy.
VPNs and extensions don’t work because the browser is ensuring your identity is constant. That’s why the large ad networks funded free/cheap CDNs.
The question (not addressed in the article) is: is there in fact a gigantic, widespread problem of using cache-sniffing to fingerprint users?
We have always known that this was possible, yet continued to include cross site caching anyway because of the enormous benefits. Presumably something fairly major has recently happened in order for this functionality to be removed- if so what?
Safari (who make a big deal about being privacy-conscious) was the first to introduce cache partitioning, looking into it as far back as 2013[1]; Chrome followed in 2020 and Firefox in 2021[3]. One thing I know, anecdotally, to be a strong motivator among browser vendors is ‘X is doing it, why aren’t we?’
1. https://bugs.webkit.org/show_bug.cgi?id=110269
2. https://developer.chrome.com/blog/http-cache-partitioning
3. https://blog.mozilla.org/security/2021/01/26/supercookie-pro...