Non-HTML Links

[Martin Atkins]

As I understand it, currently the way to bind to an identity server is 
through an HTML link element:

<link rel="openid.server" href="http://www.mydomain.com/openid" />

It seems a shame to bind Yadis to HTML, though. It would be nice (in my 
opinion, at least) to provide a mechanism which binds any URL, whatever 
media type it may point at, to an identity server.

The best I've come up with so far is the Link HTTP header, which 
performs a similar purpose to the HTML LINK element. I don't think it 
was ever formally standardised, but there exists a draft describing it:
     <http://www.w3.org/Protocols/9707-link-header.html>

While I'm hesitant to recommend implementing an un-standardized draft, 
the description there essentially mimics the HTML LINK element so I 
can't see how it could be used any differently.

This would of course be *in addition* to supporting the LINK element in 
HTML and XHTML documents, as indicated by the Content-type of the 
response. Some users are unfortunate enough to have inflicted on 
themselves hosting servers where they cannot control the HTTP headers 
returned.

Some thought should also be given to what happens in the case where 
there are multiple identity server links (HTTP or HTML), especially 
where both the HTTP header and the HTML document specify different 
servers. A given document could potentially have serveral identity 
servers vouching for it, with the intention that the consumer will trust 
one or more of them.

Better ideas than this unstandardized HTTP header are welcomed, of course.