[OpenID] The complexity of OpenID, and imperfect RPs

[James Tindall]

I'm not sure encouraging developers to stick with existing libraries is 
the best way to improve the quality of OpenID implimentations?
I suspect there will always be some developers who want to roll their 
own and so perhaps what's also needed is better documentation to help 
these developers write cleaner and more secure implimentations.

I must admit, having recently implimented an RP library myself, I often 
found the spec documents lacking and confusing in places and wondered if 
the clarity of the specs might not be improved by separating the specs 
for the RP and the OP into separate documents? Perhaps that way more 
detail specific to the RP and the OP could be added to each document 
without creating further confusion? A check list of common security 
vulnerabilities to test for would also be very usefull.

=james.tindall


Andrew Arnott wrote:
> I have been shifting my identity to my own i-name, and adding several
> authentication SEPs so that regardless of which RP I sign into, a supported
> OP ought to be found in my list (if the RP were to use a whitelist for
> example).  In theory, it's really cool.  I can log in as =Arnott anywhere
> (that takes OpenID) and my CanonicalID is used so my identity is secure for
> my whole life.  Great... in theory.
>
> Here are some of the harsh realities I've encountered while trying to live
> in this ideal situation:
>
>    1. The RP selects the wrong OP from the XRDS document (it supports
>    any/all of the OPs, but chooses the first listed one rather than the one
>    with the best priority rating).
>    2. The RP attempts authentication against one of my OPs (whether it's my
>    preferred one or not) and fails, whether it's a discovery failure, an
>    assertion verification failure, or whatever.
>    3. Although many RPs can authenticate me as =Arnott, the ones that can't
>    I try http://blog.nerdbank.net, which includes both an XRDS refererence
>    and the standard OpenID LINK tags.  If this succeeds, now I've got to
>    remember which sites I've logged into as =Arnott vs. blog.nerdbank.net.
>    If this fails, then I can choose to either surrender my attempt at using my
>    own personalized identifier and start trying my individual OP-assigned
>    identifiers, or just give up and leave the RP.
>    4. Upon successful authentication, the RP incorrectly stores my
>    user-supplied identifier (=Arnott) instead of my claimed identifier
>    (=!9B72.7DD1.50A9.5CCD).  Since I have no/little way of realizing this, I
>    naively believe that my identity on this site is secure, but when I
>    eventually surrender my =Arnott i-name for another one but keep my
>    CanonicalID, the site doesn't recognize me as the same person, and worse,
>    someone else assumes my identity.
>    5. Many RPs choose to use their own home-spun minimal implementation of
>    OpenID that is full of security holes (I've seen plenty).  As a logging in
>    user, I have no way to know whether this is a decent implementation of
>    OpenID that I'm logging into or not.  If I doubt it at all, then I must
>    assume that anyone else can spoof my identity on this site by exploiting one
>    of the many bugs common in these home spun implementations.
>
> Correctly processing an XRDS document in a fully XRDS spec-compliant way is
> no small task, and I'd wager that most or all of the OpenID libraries do not
> do it perfectly.  This means that any user trying to make the most of OpenID
> will likely be unable to log into some RP web sites, or perhaps may be able
> to but be unaware that the RP incorrectly interpreted the XRDS doc and
> stored something wrong about his identity.
> *
> Suggestions*
> It seems to me that if an RP doesn't want to risk losing visitors due to
> their unexpected or perhaps buggy identifiers/OPs, an RP should probably
> have a list of known-compatible OPs on any authentication error page it
> might display.
> I have a suggestion for the other problem(s), but I'm still working out
> details.  I may propose it to this list soon.
>
> In the meantime, does anyone else have thoughts regarding how to help solve
> these problems?  Obviously, "implement the spec correctly" is the trivial
> answer.  I'm looking for ideas on how to promote reuse of
> libraries<http://blog.nerdbank.net/2008/04/argument-for-extra-dependency-of.html>rather
> than home-spun implementations, and how to assure users that the
> right things are happening behind the scenes at the RP so that he/she can
> trust the site.
>
>   
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