Re: [Unbearable] Sec-Token-Binding header and Vary
Martin Thomson <martin.thomson@gmail.com> Wed, 04 April 2018 06:47 UTC
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From: Martin Thomson <martin.thomson@gmail.com>
Date: Wed, 04 Apr 2018 16:47:51 +1000
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To: Nick Harper <nharper@google.com>
Cc: IETF Tokbind WG <unbearable@ietf.org>
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Subject: Re: [Unbearable] Sec-Token-Binding header and Vary
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That doesn't require any more text than what is already in RFC 7234 though :) On Wed, Apr 4, 2018 at 4:04 AM, Nick Harper <nharper@google.com> wrote: > Sure, I think it's reasonable to assume that most resources depending > on token bindings (or in response to a request with Sec-Token-Binding) > would be marked Cache-Control: private, or at least not have Vary: > Sec-Token-Binding, but even if that's the common case, spec-compliant > implementations still need to handle Vary: Sec-Token-Binding (rare as > it is) if that's something the spec allows. > > On Mon, Apr 2, 2018 at 11:19 PM, Martin Thomson > <martin.thomson@gmail.com> wrote: >> ...or say nothing. >> >> ...or observe that most resources that depend on token bindings will >> be marked Cache-Control: private. >> >> On Fri, Mar 30, 2018 at 8:20 AM, Nick Harper <nharper@google.com> wrote: >>> The Vary HTTP header specifies a list of headers whose values must >>> match for a resource to be served from the cache. HTTPSTB specifies >>> that a server MAY list Sec-Token-Binding in a Vary response header. I >>> think this behavior is silly, and we should disallow Sec-Token-Binding >>> in Vary. >>> >>> The reason why this is silly is that the Sec-Token-Binding header's >>> value is dependent on the underlying connection, and it will be >>> different for requests on different connections. >>> >>> Consider a request to example.com for resource foo, sent with the >>> Sec-Token-Binding header, that gets a response with "Vary: >>> Sec-Token-Binding", and a browser caches this response. The browser >>> then visits some page that includes resource foo, so it goes to see if >>> it can use it from cache. (Assume arguendo that all other caching >>> properties are such that if there weren't this Vary header the >>> response would be served from cache.) There are two options now: >>> >>> 1) The browser has no connection open to example.com. Any attempted >>> request for resource foo would have a different Sec-Token-Binding >>> header (because it cannot possibly match the header of the request >>> sent on a different connection), so the resource cannot be loaded from >>> cache because the Sec-token-Binding header can't match. >>> 2) The browser does have a connection open to example.com. Now, the >>> browser needs to check that if it were to make a request to >>> example.com for foo, whether the Sec-Token-Binding header it would >>> generate matches - if so it can serve the response from cache; if not, >>> it needs to continue sending the request on the network. >>> >>> A main reason for caching responses is so that they can be served >>> without ever going to the network. This now requires binding a request >>> to a particular network connection before evaluating whether it can be >>> served from the cache, which seems backwards and somewhere between >>> annoying and impossible to implement. >>> >>> I suggest changing the "MAY" to "MUST NOT": Under "Additionally, the >>> Sec-Token-Binding header field:" where it says "MAY be listed by a >>> server in a Vary response header field", change this to a "MUST NOT". >>> >>> _______________________________________________ >>> Unbearable mailing list >>> Unbearable@ietf.org >>> https://www.ietf.org/mailman/listinfo/unbearable
- [Unbearable] Sec-Token-Binding header and Vary Nick Harper
- Re: [Unbearable] Sec-Token-Binding header and Vary Amos Jeffries
- Re: [Unbearable] Sec-Token-Binding header and Vary Nick Harper
- Re: [Unbearable] Sec-Token-Binding header and Vary Nick Harper
- Re: [Unbearable] Sec-Token-Binding header and Vary Martin Thomson
- Re: [Unbearable] Sec-Token-Binding header and Vary Nick Harper
- Re: [Unbearable] Sec-Token-Binding header and Vary Martin Thomson