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Re: [AC] Access Control Algorithm

From: Anne van Kesteren <annevk@opera.com>
Date: Mon, 07 May 2007 17:31:17 +0200
To: "Jonas Sicking" <jonas@sicking.cc>
Cc: "WAF WG (public)" <public-appformats@w3.org>
Message-ID: <op.tryqqfn764w2qv@id-c0020.oslo.opera.com>

On Thu, 03 May 2007 15:33:12 +0200, Jonas Sicking <jonas@sicking.cc> wrote:
> Anne van Kesteren wrote:
>>  On Thu, 03 May 2007 13:24:01 +0200, Jonas Sicking <jonas@sicking.cc>  
>> wrote:
>>> I know, but I propose we change that since I think the current  
>>> algorithm is hard to easily see what results it produces, as you  
>>> described in the initial mail in this thread.
>>
>>  With the algorithm you are proposing now that is true as well, fwiw.
>
> What is true?

That it's hard to see what the results will be. Because for a same-origin  
request a deny rule won't have any affect. In fact, the whole algorithm  
wouldn't apply.


>> Because even though it can say deny= in the processing instruction that  
>> isn't actually true for same-origin requests for instance.
>
> That is going to be true for any solution we are building, so I don't  
> see how that is an argument for or against any algorithm.

It was not an argument against the algorithm.


>> And for non same-origin requests the default is deny. Therefore the  
>> allow / exclude mechanism makes sense.
>
> Just using allow/exclude will not cater for all usecases I brought up in  
> my initial proposal, i.e. that you want to be able to, using headers,  
> deny access to all files from all or a set of remote servers.

Yes, my proposal was to allow "deny <rules> exclude <rules>" in addition  
on HTTP headers.


Having said that...

> [...]
>
> Have "allow", "deny" and "default". There is no "exclude". Order is  
> important. If headers say "deny" then immediately deny. If headers say  
> "allow" or "default" check with PIs. If PIs say "deny" deny. If PIs say  
> "allow" allow. If PIs say nothing and headers said "allow" allow.  
> Otherwise deny.
>
> If we allow "default" in PIs or not doesn't really matter to me. In the  
> end they are useless, but it would be consistent.

So what would happen for:

   Content-Access-Control: allow <*.bar.com>, deny <*.bar.com>

You seemed to imply that ordering was important, but I wonder if that's  
intuitive. I would personally be fine with your proposal though. I'm not  
sure Thomas Roessler would be, but then he didn't chime in anymore to  
argue about it.


(I hope we can resolve this soonish (though it's mostly me that's lacking  
in fast replies, sorry about that) so I can update the algorithm once  
again and get the specification re-published.)


-- 
Anne van Kesteren
<http://annevankesteren.nl/>
<http://www.opera.com/>
Received on Monday, 7 May 2007 15:31:37 GMT

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