[OpenID] Flickr / Yahoo OpenID implementation

[Andrew Arnott]

Caution: just because you get an assertion back from an OP, that does not imply
that X trusts Z!  An OP might change the Claimed Identifier and then there's
no trust left.
For instance, a user might try to log in as X.  The OP might decide "you're
not X, but you can log in as Y if you want".  The user can say "sure", and
then the OP sends an assertion for Y.  That's legal (per my reading of the
spec), and the RP would be wrong to assume that since it asked for X and got
Y that that was "good enough".

--
Andrew Arnott
"I [may] not agree with what you have to say, but I'll defend to the death
your right to say it." - Voltaire


On Mon, Jan 12, 2009 at 9:59 PM, Luke Shepard <lshepard at facebook.com> wrote:

>  If you go to http://flickr.com/photos/benschwarz, you'll see this tag:
>
>  <link rel="openid2.provider" href="https://
> open.login.yahooapis.com/openid/op/auth" />
>
> That basically says "I authorize Yahooapis.com to say who I am". So you
> attempt to login as X, and X says "trust Yahoo", and then Yahoo says "this
> is Z". So it's still a cycle of trust.
>
>
> On 1/12/09 9:55 PM, "Ben Schwarz" <ben.schwarz at gmail.com> wrote:
>
> How can that serve as authentication?
> I've requested the user to login as x and I get a z in return? I have no
> way of telling that the user is indeed who they said they were.
>
> Thus rendering the service unusable.
>
> I'm rather surprised that this is considered part of the specification.
>
>
>
>
> On 13/01/2009, at 4:48 PM, Andrew Arnott wrote:
>
> That's the tricky bit.  See, even though you as the RP send a claimed
> identifier with a URL that is readable, once Yahoo! identifies which user is
> logged in to itself, it can negotiate with that user (or look up a previous
> setting) what claimed id to actually send back to the RP, and it may be
> different, in fact a hashed-looking URL as you're seeing.
>
> When I first saw this behavior I thought it was a bug too.  But a careful
> reading of the OpenID 2.0 spec seems to not forbid OPs from changing the
> claimed id that the RP initiated the request with.
>
>
> Although if an OP changes the claimed id when the claimed id and the
> local_id are different, then that OP just broke OpenID delegation, which I
> consider a bug.
>
> --
> Andrew Arnott
>  "I [may] not agree with what you have to say, but I'll defend to the death
> your right to say it." - Voltaire
>
>
> On Mon, Jan 12, 2009 at 9:25 PM, Ben Schwarz <ben.schwarz at gmail.com>
> wrote:
>
>
> Thanks for the quick and detailed reply Andrew.
>
> However, I am requesting auth using the Flickr address, which is a direct
> link to the identity of said user, Yahoo is indeed returning a *different*URL.
>
>
>
> On 13/01/2009, at 4:22 PM, Andrew Arnott wrote:
>
> Yahoo! is leverage something called directed identity.  It's legal per the
> spec.  It's actually optional per-user, but Yahoo offers this as a default
> specifically to prevent sites from knowing who their users are without the
> users specifically telling them.
>
> The only thing you can know when an OpenID user from Yahoo logs in using
> that hashed claimed id, is that they are the same person who logged in last
> time with that hashed URL.  No way to know who is behind the hash though.
>
>
>  --
> Andrew Arnott
> "I [may] not agree with what you have to say, but I'll defend to the death
> your right to say it." - Voltaire
>
>
> On Mon, Jan 12, 2009 at 9:17 PM, Ben Schwarz <ben.schwarz at gmail.com>
> wrote:
>
>
> Hi All,
>
>  I'm looking to implement Flickr OpenID with Yahoo, unless I've incorrectly
> understood the specification; I believe they've implemented incorrectly /
> poorly.
>
>  I make a request to auth with http://flickr.com/photos/benschwarz, which
> goes to yahoo; it allows me to auth successfully.
>  The identity url returned by default, however is something like
> http://me.yahoo.com/some-hashed-url
>
>  Without the correct identity url being returned, I have no way of knowing
> that my users are who they say they are.
>
>  Have I missed a detail in using OpenID or have Yahoo implemented poorly?
>
>
>  Cheers,
>
>
>  Ben
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