If I understand this correctly, the state of having received an Accept-CH header field in a response to a previous request is used to determine whether these new Sec-CH-* header fields will be sent. Not only does this add a new place to store bits on the client (as acknowledged by https://wicg.github.io/client-hints-infrastructure/#accept-ch-cache-definition <https://wicg.github.io/client-hints-infrastructure/#accept-ch-cache-definition> ) but it also seems to not provide a method for a server to receive client hint header fields on the first request from a client. Would both of these concerns be resolved if we used something like ALPN instead of needing to store state on the client? Am I understanding the Client Hints Infrastructure correctly?
> On Nov 2, 2020, at 3:32 PM, Maciej Stachowiak <m...@apple.com> wrote: > > > >> On Nov 2, 2020, at 8:56 AM, Yoav Weiss <y...@yoav.ws <mailto:y...@yoav.ws>> >> wrote: >> >> Thanks for re-reviewing, Maciej! >> >> Adding Mike Taylor, who's likely to take a closer look at this. >> >> On Mon, Nov 2, 2020 at 2:17 AM Maciej Stachowiak <m...@apple.com >> <mailto:m...@apple.com>> wrote: >> >> I just did a fresh review of that spec and explainer. Thanks for addressing >> many of the previous issues. This addresses many of the potential objections. >> >> Here’s the new issues I filed: >> >> https://github.com/WICG/ua-client-hints/issues/141 >> <https://github.com/WICG/ua-client-hints/issues/141> >> https://github.com/WICG/ua-client-hints/issues/142 >> <https://github.com/WICG/ua-client-hints/issues/142> >> https://github.com/WICG/ua-client-hints/issues/143 >> <https://github.com/WICG/ua-client-hints/issues/143> >> https://github.com/WICG/ua-client-hints/issues/144 >> <https://github.com/WICG/ua-client-hints/issues/144> >> https://github.com/WICG/ua-client-hints/issues/145 >> <https://github.com/WICG/ua-client-hints/issues/145> >> https://github.com/WICG/ua-client-hints/issues/146 >> <https://github.com/WICG/ua-client-hints/issues/146> >> https://github.com/WICG/ua-client-hints/issues/147 >> <https://github.com/WICG/ua-client-hints/issues/147> >> https://github.com/WICG/ua-client-hints/issues/148 >> <https://github.com/WICG/ua-client-hints/issues/148> >> https://github.com/WICG/ua-client-hints/issues/149 >> <https://github.com/WICG/ua-client-hints/issues/149> >> https://github.com/WICG/ua-client-hints/issues/150 >> <https://github.com/WICG/ua-client-hints/issues/150> >> https://github.com/WICG/ua-client-hints/issues/151 >> <https://github.com/WICG/ua-client-hints/issues/151> >> >> >> Thanks for filing those! We'll take a look and respond shortly. >> >> Most of these are minor/editorial, but I think 151 is potentially a >> deal-breaker. I may be misreading the spec, but as written >> getHighEntropyValues seems to give access to all of the high entropy client >> hints to third-party scripts in the first party context, and scripts running >> in third-party iframes, regardless of which ones the site has opted into via >> the relevant HTTP header. >> >> That's indeed the case, as we didn't consider the Client Hints opt-in to be >> something that impacts the availability of the JS API. (as it doesn't do >> that for other hints) > > We’re currently deeply skeptical of implementing any of the other client > hints due to their expansion of fingerprinting surface, so I don’t feel > particularly compelled by that precedent. That said, it’s likely the other > client hints have this same problem, where they expose fingerprinting surface > way more widely than they may be intending to. > >> That would be a huge problem, as it would grant a lot of active >> fingerprinting surface unnecessarily >> >> We did discuss >> <https://github.com/WICG/ua-client-hints/issues/37#issuecomment-576730548> >> adding a Feature Policy (now Permission Policy) to that effect. Would that >> help with your concerns? > > My understanding is that feature policy applies at the frame level, and > therefore could not be used to control what happens when a third-party script > in a first party context calls the API. Even for third-party iframes, it > seems like Feature Policy could only default-deny this JS API entirely, and > would not be able to filter the results down to the set delegated via HTTP > headers (or otherwise). Maybe you intend a feature policy per individual high > entropy hint, but first of all that seems like overkill, and second, the spec > is clearly not written to support such filtering. > > So no, it would not address the concerns. > > I think the best approach is to limit the hints to those opted into (or, in > case of a third-party frame, delegated). That or remove the script API > entirely. The origin-based delegation model that works well at the HTTP level > is not well aligned with the widespread practice of including third-party > scripts in the top frame. > > The spec does not eve allow denying the request entirely as written. A > non-normative Note suggests that is allowed, but I can’t find any step in the > algorithm that would ever reject the promise. > >> >> (perhaps even expanding beyond what is currently possible with the UA >> string). >> >> Can you expand on that last point? > > I mean that the client hints might include info that is not in the UA sting > (possibly not at all, or possibly frozen in UA string but could be unfrozen > in the client hints). > >> >> >> Regards, >> Maciej >> >> >>> On Oct 27, 2020, at 12:35 AM, Yoav Weiss <y...@yoav.ws >>> <mailto:y...@yoav.ws>> wrote: >>> >>> Yet-another ping! :) >>> >>> On Wed, Oct 7, 2020 at 8:23 AM Yoav Weiss <y...@yoav.ws >>> <mailto:y...@yoav.ws>> wrote: >>> Friendly ping! :) >>> >>> On Wed, Sep 30, 2020 at 9:29 AM Yoav Weiss <y...@yoav.ws >>> <mailto:y...@yoav.ws>> wrote: >>> Hi WebKit folks, >>> >>> Circling back on the previous discussion >>> <https://lists.webkit.org/pipermail/webkit-dev/2020-May/031195.html> about >>> User-Agent ClientHint. The feature was implemented in Chromium and is being >>> rolled out in Chrome. >>> >>> There were some concerns mentioned in the previous thread, that we believe >>> were since addressed. Would the feature be something that WebKit would >>> consider shipping? >>> >>> Cheers :) >>> Yoav >>> _______________________________________________ >>> webkit-dev mailing list >>> webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> >>> https://lists.webkit.org/mailman/listinfo/webkit-dev >>> <https://lists.webkit.org/mailman/listinfo/webkit-dev> > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev
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