Re: Working Group Last Call: HTTP Client Hints
Yoav Weiss <yoav@yoav.ws> Mon, 24 February 2020 08:05 UTC
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From: Yoav Weiss <yoav@yoav.ws>
Date: Mon, 24 Feb 2020 09:01:02 +0100
Message-ID: <CACj=BEgUzcHDPEwc8WpjTwSotqhDw6ubQTU_fcaTddTZPacncg@mail.gmail.com>
To: Julian Reschke <julian.reschke@gmx.de>
Cc: Mark Nottingham <mnot@mnot.net>, HTTP Working Group <ietf-http-wg@w3.org>, Tommy Pauly <tpauly@apple.com>
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Subject: Re: Working Group Last Call: HTTP Client Hints
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Thanks for your feedback, Julian! I PRed the related changes at https://github.com/httpwg/http-extensions/pull/1072 On Sun, Feb 23, 2020 at 2:20 PM Julian Reschke <julian.reschke@gmx.de> wrote: > On 18.02.2020 05:09, Mark Nottingham wrote: > > ... > > Here's my feedback: > > Terminology: please use "header field" or "field" consistently. > Done. > > In Section 1: > > well as dynamic user and client preferences. Applications that want > to allow the server to optimize content delivery and user experience > based on such capabilities have, historically, had to rely on passive > identification (e.g., by matching User-Agent (Section 5.5.3 of > [RFC7231]) header field against an established database of client > signatures), used HTTP cookies and URL parameters, or use some > combination of these and similar mechanisms to enable ad hoc content > negotiation. > > Please add refernce to Cookie spec. > Sure. That would be a reference to https://tools.ietf.org/html/rfc6265 or https://tools.ietf.org/html/draft-ietf-httpbis-rfc6265bis-05? I'm guessing the former, but preferred asking. > > However, proactive content negotiation requires clients to send these > request headers prolifically. This causes performance concerns > (because it creates "bloat" in requests), as well as privacy issues; > passively providing such information allows servers to silently > fingerprint the user agent. > > FWIW, it doesn't really *require* them to be send prolifically; it's > just the easiest way to do so. > > If there was a requirement for that, *this* spec by definition couldn't > exist. > Replaced it with "However, traditional proactive content negotiation techniques often mean that clients send these request headers prolifically." > This document defines the Client Hints infrastructure, a framework > that enables servers to opt-in to specific proactive content > negotiation features, which will enable them to adapt their content > accordingly. However, it does not define any specific features that > will use that infrastructure. Those features will be defined in > their respective specifications. > > It would be great if this could link to at least one example of those. > Linked to UA Client Hints. > > In 1.1.: > > This document uses the Augmented Backus-Naur Form (ABNF) notation of > [RFC5234] with the list rule extension defined in [RFC7230], > Appendix B. It includes by reference the DIGIT rule from [RFC5234] > and the OWS and field-name rules from [RFC7230]. > > No, it doesn't. > Removed everything but the 5234 reference. > > In Section 2: > > A Client Hint request header field is a HTTP header field that is > used by HTTP clients to indicate configuration data that can be used > by the server to select an appropriate response. Each one conveys > client preferences that the server can use to adapt and optimize the > response. > > Is it really always "configuration data"? > Removed "configuration" > > 2.1. Sending Client Hints > > Clients control which Client Hints are sent in requests, based on > their default settings, user configuration, and server preferences. > The client and server can use an opt-in mechanism outlined below to > negotiate which fields should be sent to allow for efficient content > adaption, and optionally use additional mechanisms to negotiate > delegation policies that control access of third parties to same > fields. > > Implementers should be aware of the passive fingerprinting > implications when implementing support for Client Hints, and follow > the considerations outlined in "Security Considerations" section of > this document. > > General comment: it seems to me that BCP14 keywords are uppercased > somewhat randomly... > Renamed a few instances that were not meant to be used in the BCP14 keyword sense, and capitalized others. > > Implementers should be aware of the passive fingerprinting > implications when implementing support for Client Hints, and follow > the considerations outlined in "Security Considerations" section of > this document. > > Please make this a proper xml2rfc link... > Added a link. > > > Section 3.: > > Servers can advertise support for Client Hints using the mechnisms > described below. > > a) a/mechnisms/mechanisms/ > b) looks like a single mechanism to me, actually > Good catch, thanks! > > > In 3.1: > > The Accept-CH response header field or the equivalent HTML meta > element with http-equiv attribute ([HTML]) indicate server support > for particular hints indicated in its value. > > A more precise reference might be good here. The HTML spec is really big. > Sure! Added a section number. Not sure how to link directly to specific anchors in other specs. > Accept-CH is a Structured Header [I-D.ietf-httpbis-header-structure]. > Its value MUST be an sh-list (Section 3.1 of > [I-D.ietf-httpbis-header-structure]) whose members are tokens > (Section 3.7 of [I-D.ietf-httpbis-header-structure]). Its ABNF is: > > There is no Section 3.7 there; maybe > < > https://tools.ietf.org/html/draft-ietf-httpbis-header-structure-15#section-3.3.4 > >? > Indeed. > > Accept-CH = sh-list > > For example: > > Accept-CH: Sec-CH-Example, Sec-CH-Example-2 > > When a client receives an HTTP response advertising support for > provided list of Clients Hints, it SHOULD process it as origin > ([RFC6454]) opt-in to receive Client Hint header fields advertised in > the field-value, for subsequent same-origin requests. > > RFC6454 appears as informative reference, but has a normative > requirement referencing it. > Added a "!" > > For example, based on the Accept-CH example above, which is received > in response to a user agent navigating to "https://example.com", and > delivered over a secure transport: a user agent SHOULD persist an > Accept-CH preference bound to "https://example.com" and use it for > user agent navigations to "https://example.com" and any same-origin > resource requests initiated by the page constructed from the > navigation's response. This preference SHOULD NOT extend to resource > requests initiated to "https://example.com" from other origins. > > Don't put normative keywords into examples. The requirements are alreay > defined earlier, right? For instance, say "will have to" instead of > "SHOULD". > Changed. > > In 3.1.1: > > I'd make that Section 3.2. > > In 4.1: > > o Entropy > > * Exposing highly granular data may help identify users across > multiple requests to different origins. Reducing the set of > field values that can be expressed, or restricting them to an > enumerated range where the advertised value is close but is not > an exact representation of the current value, can improve > privacy and reduce risk of linkability by ensuring that the > same value is sent by multiple users. > o Sensitivity > > * The feature SHOULD NOT expose user sensitive information. To > that end, information available to the application, but gated > behind specific user actions (e.g. a permission prompt or user > activation) SHOULD NOT be exposed as a Client Hint. > o Change over time > > * The feature SHOULD NOT expose user information that changes > over time, unless the state change itself is also exposed (e.g. > through JavaScript callbacks). > > The list is structured a bit strange. Maybe make it a definition list. > Can you point to an example of what you mean by that? > > > Appendix A. Interaction with Variants Response Header Field > > Client Hints may be combined with Variants response header field > [VARIANTS] to enable fine-grained control of the cache key for > improved cache efficiency. Features that define Client Hints will > need to specify the related variants algorithms as described in > Section 6 of [VARIANTS]. > > Unless we're planning to finish VARIANTS really soon, I'd drop this > appendix. > mnot - thoughts?
- Working Group Last Call: HTTP Client Hints Mark Nottingham
- Re: Working Group Last Call: HTTP Client Hints Julian Reschke
- Re: Working Group Last Call: HTTP Client Hints Tommy Pauly
- Re: Working Group Last Call: HTTP Client Hints Julian Reschke
- Re: Working Group Last Call: HTTP Client Hints Yoav Weiss
- Re: Working Group Last Call: HTTP Client Hints Mark Nottingham
- Re: Working Group Last Call: HTTP Client Hints Yoav Weiss
- Re: Working Group Last Call: HTTP Client Hints Mark Nottingham
- Re: Working Group Last Call: HTTP Client Hints Yoav Weiss