Re: [http-state] Assumed Vary: Cookie

Julian Reschke <julian.reschke@gmx.de> Fri, 21 November 2014 14:25 UTC

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Date: Fri, 21 Nov 2014 15:24:44 +0100
From: Julian Reschke <julian.reschke@gmx.de>
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To: Bjoern Hoehrmann <derhoermi@gmx.net>, Anne van Kesteren <annevk@annevk.nl>
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Cc: Boris Zbarsky <bzbarsky@mit.edu>, http-state@ietf.org
Subject: Re: [http-state] Assumed Vary: Cookie
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On 2014-11-21 15:13, Bjoern Hoehrmann wrote:
> * Anne van Kesteren wrote:
>> RFC 6265 does not really explain the relationship to the HTTP cache
>> and how this is somewhat special for cookies. In particular,
>> implementations assume that a different value for the Cookie request
>> header means the cache cannot be reused. Can errata be issued?
>>
>> For additional context:
>>
>>   http://lists.w3.org/Archives/Public/ietf-http-wg/2009AprJun/0464.html
>>   https://bugzilla.mozilla.org/show_bug.cgi?id=1075297#c5
>
> It seems that implementations vary in what assumptions they make about
> server responses when sending or omitting a `Cookie` header in requests.
> Even for the dominant web browsers there does not seem to be a common
> reliable behavior, and I am sure there are non-browser caches that do
> not assume `Vary: Cookie`. So it's not obvious to me what the document
> should say on the matter.

What it currently says is (a) intentional and (b) consistent with the 
relevant HTTP spec 
(<http://greenbytes.de/tech/webdav/rfc6265.html#rfc.section.3.p.3>):

"The presence of a Cookie or a Set-Cookie header field does not preclude 
HTTP caches from storing and reusing a response."

Furthermore, Anne says:

"...that a different value for the Cookie request header means the cache 
cannot be reused. ..."

If a resource varies on "Cookie", it will also vary on the *absence* of 
Cookie (which in general would imply non-authenticated access if the 
cookie was used to identify the user). So that would need to be made 
very clear.

I'm ok with a potential revision of RFC 6265 *mentioning* the caching 
heuristics that are in common use, but right now I don't see a normative 
requirement coming out of that.

> (And as an aside, for the specific bug report above, it seems Chrome's
> behavior is better than that of Firefox, but Mozilla does not seem in-
> terested in aligning their implementation with Chrome in this regard.)

Pointer?

Best regards, Julian