On Wed, Oct 28, 2020 at 4:56 PM Reilly Grant <reillyg@google.com> wrote:

I would like to request an official position from the WebKit team on the emerging Idle Detection API specification. I am aware that this API was included in a list of APIs which you have decided not to implement due to fingerprinting concerns. I assume that this objection was based on the original explainer provided for this API.

Our position has not changed. Our concerns are not limited to fingerprinting. There is an obvious privacy concern that this API lets a website observe whether a person is near the device or not. This could be used, for example, to start mining bitcoins when the user is not around or start deploying security exploits, etc...

Since that list was posted the API has been extended to include a permission that sites must acquire before being granted access to user presence signals. I would like to start a conversation to understand the fingerprinting risks you foresee from this API.

This kind of action-at-a-distance permission prompt is problematic because it's unclear to the user why such a permission should be granted and for what purpose.

Additionally, the use cases listed at https://github.com/WICG/idle-detection/blob/master/README.md are rather weak.

Chat application: presenting a user's status to other users and delivering notifications to the device where the user is active.

Why does delivering a notification to all devices considered bad? That's what happens to most notifications I receive and modern operating systems have ways to hide & dismiss old notifications anyway. It's also unclear how users are supposed to know of this use case when assessing whether to allow a permission for this API or not.

Showing timely notifications - e.g. deferring displaying feedback until the user returns to an active state.

Again, it's unclear why this is desirable. If I'm not at a computer, it's okay for the notification to still arrive. I'd see it when I come back to my computer.

Updating an outdated service worker when there's no unsaved state by triggering reloading of the tab.

This doesn't seem like something you'd need idle detection API to do. It's sufficient to realize that you haven't recently received user inputs on your website. I have plenty of tabs & windows that I don't touch for hours if not days. Any websites loaded in such browsing contexts should consider doing that kind of updates / synchronization. If the argument is that the user may go back to such tabs / windows if they're currently present, then this user idle detection API won't help either because the user may come back to it at any moment.

- R. Niwa