Sxip concerns with YADIS

Dick Hardt dick at
Sun Dec 18 08:36:58 UTC 2005


Thanks for the response.

I don't understand the user-driven vs service provider driven  
adoption point you make, nor how it relates to requiring two URLs.

Yes, there are lots of XML parsers. Does not mean you need to use  
XML. HTML is a nice, structured format that is heavily used as well.

I don't understand your fine-grained YADIS capabilities point either.  
And the only thing that makes sense to be PULLed is data that someone  
wants to make public, but that is another debate.

Summary: you have not convinced me that there are any advantages to  
the current spec (you can do everything you want to do given my  
suggestion), and I have pointed out several significant advantages.

-- Dick

On 17-Dec-05, at 11:38 PM, Johannes Ernst wrote:

> Dick,
> first: it's great that you are seriously looking at YADIS. Welcome  
> to YADIS!
> second: it's even better that you are looking at the currently  
> proposed protocols/formats, and that you are willing to provide  
> feedback on them. That keeps us honest and having additional  
> competent people, like yourself, critically review what we're up to  
> is definitely A Good Thing, regardless of whether any particular  
> suggestion will be adopted or not. Thank you!
> I think the issues you raise are valid ones, and they have been  
> discussed pretty exhaustively since Brad, David and myself  
> originally started meeting. The reasons why we came down to the  
> tradeoff -- because that's what it is -- that we came down to have  
> to do with the somewhat conflicting goals of enabling both user- 
> driven (passive service provider) and service-provider (passive  
> user) adoption. Note that in the best case scenario, only a single  
> HTTP GET is necessary, although you are correct in observing that  
> in practice during the early years of adoption, many times it will  
> have to be two GETs. (I realize that these scenarios are woefully  
> underdocumented at this point, and it's difficult for somebody  
> joining the discussion in the middle like yourself to get a  
> cohesive and complete picture right now of what those tradeoffs  
> were -- sorry about that, but we're working on it, and rest assured  
> that there are valid arguments behind those).
> Re XML parser, the first public YADIS draft actually used plain  
> text, not XML, but so many people were arguing convincingly that  
> all platforms have good XML parsers at this point and that we want  
> to develop a forward-looking standard, not a backward-looking one.  
> Hard to argue with that ;-), particularly given the beauty of XPath  
> for evaluating YADIS/XRDS documents.
> Re the very idea of fine-grained YADIS capabilities, of course we  
> think there's a need for it!! Without it, or something technically  
> equivalent, how could we, say, use OpenID authentication for the  
> client in a LID query for somebody's cell phone number? One of the  
> goals of YADIS is to let identity-related innovation occur on a  
> capability level rather than on a "vertically integrated identity  
> system" level, so that scenarios like this hybrid cell phone number  
> query are possible and commonplace. Our design principle here is  
> "small pieces loosely joined", rather than "big pieces that need to  
> be swallowed whole ..." While we've never talked about this as far  
> as I remember, I'd rather expect -- given that the existing "big"  
> standards for identity haven't been able to meet so many people's  
> needs, which of course is also the reason d'être for SXIP -- that  
> you'd agree with us on that one?
> Cheers,
> Johannes.
> On Dec 17, 2005, at 20:05, Dick Hardt wrote:
>> We spent some time looking at YADIS to see how a persona-url could  
>> support multiple identity protocols, specifically, how could  
>> someone have a persona-url that worked with SXIP and the protocols  
>> currently working with YADIS.
>> We think that the blogosphere will likely be the source of many of  
>> the early adopters of an identity system, and that the URL of  
>> their blog is something they think of as being part of their  
>> identity, and is one of their personas. The URL is a unique  
>> identifier, and we call it a persona-url.
>> The persona-url points to an HTML page that contains markup that  
>> allows an identity system to discover information about the  
>> persona. YADIS is about allowing Relying Partys (RP) to understand  
>> what protocol a persona-url supports.[1]
>> The YADIS Capability Discovery Protocol [2] requires the persona- 
>> url to return either an HTML page that contains a link  
>> (capabilities-url) to an XRDS XML file , or an XRDS XML file
>> Assuming the premise that most persona-urls will point to HTML  
>> pages, most of the time the RP will have to fetch two documents,  
>> and that *ALL* RPs will have to have an XML parser.
>> 1) Performance
>> 	- double the number of GETs for all HTML persona-urls
>> 	- XML parsers take time to load and parse a file
>> 2) Security
>> 	- the user needs control over both the pesona-url AND the  
>> capabilities-url to secure their identity. Double the URLs, double  
>> the risk.
>> 3) Implementation
>> 	- all major web development platforms have high performance HTML  
>> parsers that present the document as a DOM. XML parsing is common,  
>> but is more complex than manipulating a DOM, and another thing for  
>> the developer to figure out.
>> 	- getting two files requires more code, and more chances of  
>> something being broken
>> We liked the way that OpenID worked earlier with a LINK tag in HTML:
>> 	<link rel="openid.server" href="" >
>> We will have a LINK tag that looks something like this:
>> 	<link rel="dix-homesite" href=" 
>>" class="dix:/core#1 dix://" >
>> And think that LID could have a tag like this:
>> 	<link rel="lid.capabilities"  type="application/xrds+xml"  
>> href="">
>> Given that most protocols will have their own ways of describing  
>> what it can do, we don't see value in a common capability file.
>> [1]
>> [2]
> Johannes Ernst
> <lid.gif>

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