[OpenID] Summarizing my grouse with XRD

[John Bradley]

XRD is a XML document spec.

On 2009-10-21, at 5:21 PM, John Kemp wrote:

> John Bradley wrote:
>> It means that some protocol that is using XRD is defining the  
>> subject via some external mechanism.
>
> So the XRD spec. is a template spec. meant to be simply incorporated  
> by reference into other specs. I guess?
>
Like other XML specs eg SAML 2.0 it can be used multiple  
specifications that process XML documents.

External specs can profile the XRD spec.

>> In the HTTP protocol case there may be an implicit subject based on  
>> the identifier that is being resolved.
>
> As mentioned earlier, if the _subject_ of the XRD is identified  
> (implicitly) by the same URI used to retrieve the XRD itself, then  
> that seems rather circular.
>
The XML document describes a resource and provides links to associated  
resources.
A HTML page doesn't need to explicitly say what URI it is retrieved  
from in its internal markup.

Like with HTML sometimes the subject is defined by the transport or  
other external method.

Thanks
John B.
>> All normal http caching would apply in the http: case.
>
> Sure, I'm not quibbling with caching...
>
>> In the IMI/SAML case we have discussed pushing a XRD as a assertion/ 
>> claim.
>> In that case the subject may be the same as the saml:NameID in the  
>> containing saml:Assertion.
>> It could perhaps be argued that putting a xrd:Subject and signature  
>> inside a signed saml:Asertion is un-neccicary.
>> Suffice to say it is up to the protocol using XRD to decide what to  
>> make of a XRD without a xrd:Subject.
>
> OK, I think I've understood ;)
>
> Cheers,
>
> - johnk
>
>> John B.
>> On 2009-10-21, at 3:09 PM, John Kemp wrote:
>>> John Bradley wrote:
>>>> Yes a XRD can be used for identity.  In that case it should be a  
>>>> signed XRD (with Subject)
>>>> However a XRD can be used to describe any resource (URI).
>>>
>>> What does it mean then (in XRD terms) if an XRD doesn't identify  
>>> the resource it describes (ie. it doesn't have a subject)?
>>>
>>> - johnk
>

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