Request for position on First-Party Sets

# Lily Chen (9 days ago)


We are requesting WebKit's position on the First-Party Sets proposal as described in the explainer [1]. Feedback [2] was provided on a previous version of the proposal, which has since been revised. The TAG review thread is here [3].


[1] Explainer: krgovind/first-party-sets [2] Previous feedback: krgovind/first-party-sets#6 [3] TAG review: w3ctag/design-reviews#342

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# Maciej Stachowiak (9 days ago)

(1) I notice that this proposal still exists only in a random personal repo. Could it please be contributed to an appropriate standards or incubation group? Privacy CG would almost certainly welcome this, and I’m sure it would be easy to move to WICG as well. There doesn’t seem to be a reason to keep the proposal in this “pre-incubation” state.

(2) As discussed in the Privacy CG Face-to-Face, there are two key problems to solve with First Party Sets or any similar proposals: (a) Bad faith claims. How to prevent domains that are not actually owned and controlled by the same party from making claims of being related? For example, an ad network could get its top publishers to enter an association to regain a certain level of tracking powers. (b) The “500 domains” problem. If a first party owns domains that aren’t obviously related and that appear to different and distinct brands to the user, then the user won’t expect to be tracked across them. (Problem named such because of a party known to have hundreds of domains that mostly appear to be totally distinct brands). Users would expect both transparency and control over this.

The explainer does not really give solutions to these problems. Rather, it defers entirely to each individual browser to define a policy to solve these problems. Deferring to individual browsers on such key points is problematic in a few ways: (i) It doesn’t seem right for a proposed web standard to solve only the easy problem of syntax, and leave the hardest technical problems of semantics to each browser separately. (ii) Deferring in this way is bad for interop. (iii) It’s not entirely clear if there exists any policy that suitably addresses these problems. By only speculating about policies, the explainer fails to provide an existence proof that it is implementable. (iv) If sites come to depend on First Party Sets for correct behavior, there is a risk that every UA will have to adopt a policy that’s the most permissive of any, or that copies the most popular UA, for the sake of compatibility. Thus, leaving this open may not in fact provide a useful degree of freedom.

Given these issues, I don’t think we’d implement the proposal in its current state. That said, we’re very interested in this area, and indeed, John Wilander proposed a form of this idea before Mike West’s later re-proposal. If these issues were addressed in a satisfactory way, I think we’d be very interested. It does seem that binding strictly to eTLD+1 is not good enough for web privacy features. Driving these issues to resolution is part of why we’d like to see this proposal adopted into a suitable standards or incubation group.

# Maciej Stachowiak (a day ago)

On Jun 3, 2020, at 5:21 PM, Kaustubha Govind <kaustubhag at> wrote:

Hi Maciej,

Thanks for feedback.

We had previously started the incubation process in WICG, and it was just moved there: WICG/first-party-sets, WICG/first-party-sets

In addition, I have also filed a Proposal Issue in PrivacyCG: privacycg/proposals#17, privacycg/proposals#17

Thanks! I expressed support for the above proposal.

Regarding your concern about preventing (a) Bad faith claims, and (b) The “500 domains” problem. These are absolutely cases that we would consider "unacceptable sets", and our initial thinking was that this would be covered by the "UA Policy" and be subject to review during the acceptance/verification process. In this version of the proposal, we attempted to build maximum flexibility for UAs; but it has since become clear that browsers find this problem worth solving, and also deem it important to agree on a common policy. We are currently working on an initial draft of a policy, and will bring that for discussion when ready.

That sounds like a positive development, looking forward to it.

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