I've not double checked what the spec has to say about this Andrew but it seems to me that if an association with the chosen OP exists and is alive then the RP should simply attempt authorization using 'checkid_immediate' and if that then fails the RP should try authentication using the next endpoint in the list?

Andrew Arnott wrote:

Another thought: since a responsible RP only creates a single association
with an OP and stores it until it expires, and these associations often last
days, if the user has an endpoint in the XRDS doc that points to an OP that
is currently down, but with whom the RP has an existing, unexpired
association with, the RP shouldn't try to create an association with that
OP.  Instead, it might say to itself "yes, I successfully have an
association with this OP, so I'll redirect the user to it", but the OP
happens to be down for 5 hours that day, effectively disabling the user's
ability to log in, in spite of the multiple OPs listed in the XRDS doc.

So... perhaps OpenID can have a "ping, are you alive?" message in its
protocol.  But then we're no better than "dumb" RPs having to make multiple
hits to the OP instead of just one.

Another idea that keeps occuring to me is that the RP can use a frameset to
keep an RP frame around and have the OP authentication happen in another
frame (iframe or frameset would work).  That way, the RP frame could have
something like "Is your Provider not responding?  Click here to try your
next best choice..." or something to that effect.  The problem with this
idea is that the URL on the browser will always be the RP, so the user will
have one less way to confirm that this is indeed his genuine Provider and
not one of those notorious OpenID RP phishing attacks.

Anyone have any idea how to solve this dead OP problem?

On Tue, Jul 15, 2008 at 1:52 AM, James Tindall <james <at> atomless.com> wrote:

 

I've recently been writing an openid relying party library for the
Kohana php framework and I think you're right, the way I've tried to
handle multiple enpoints returned from the discovery phase is to first
sort them by their priority values and then also filter out any that do
not meet the (extension / security / openid-version) requirements set in
the current relying party configuration and then finally attempt to
establish an association with each endpoint in turn until a successfull
association response is returned.

I feel that all this is best done invisibly rather than requesting the
user to jump through extra hoops. The user has after all -at some point-
set the priority of the endpoints listed in the xrds and I suspect that
most would not wish for further input during the process of
authentication. My assumption being that the point of multiple endpoints
is to hopefully cater for the requirements of as many different relying
parties as possible and to have alternative/backup endpoints incase of
errors or failures with any of the other endpoints in the list during
authentication?

=james.tindall

Andrew Arnott wrote:
   

I'm curious how other libraries do (or plan to) handle multiple endpoints
     

in
   

a single XRDS document.  I see a few considerations, in order:

  1. Enumerate the services in the XRDS-defined priority order
  2. Skip the services that do not expose OpenID endpoints.
  3. Skip the OpenID endpoints with Providers that do not quality
  (whitelist/blacklist or advertised extension support
  4. Take the first endpoint that is left after these filters.

But what about the rest of the endpoints listed?  Here are some
possibilities:

  1. Just use the first endpoint and trust it works.
  2. Try each one successively.  That is, the RP should attempt to
  establish an association with each one until it succeeds with one, and
     

then
   

  redirect the user to that one for authentication.  Redirecting the
     

user to
   

  an unavailable Provider will result in a dead end failure page and the
     

RP
   

  will lose the opportunity at this point to try the next endpoint.
  3. A variant on the last, except that in addition to skipping OPs that
     

do
   

  not respond to association requests, allow the user to "fail" or
     

cancel the
   

  authentication on the first provider and proceed to the second
     

provider
   

  listed for another authentication attempt.
  4. Offer the user a list of his/her providers to choose from for
  authentication.

Have thoughts been written already on which of these are best and/or
     

common
   

in existing libraries?


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T : +44(0)1305 250 377
M : +44(0)7971 012 032
F : +44(0)1305 250 377

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