Thanks for the reply...some comments in-line!
On Fri, Aug 15, 2008 at 6:26 AM, James Henstridge [EMAIL PROTECTED]wrote:
2008/8/15 Scott Battaglia [EMAIL PROTECTED]:
snip /
1. Do you guys support accessing a service on behalf of a user. In CAS
we
call this proxying on behalf of the user. But essentially, if you're
say, a
portal, and you need to access the grades, you would retrieve a CAS proxy
ticket and give it to the grades service which would resolve that to the
user as well as the chain of where it came from.
There are a few models that can be used for this:
1. The user goes to the grades service and requests that their data
get transferred to the OpenID provider via the attribute exchange
protocol. When they go to the portal site, the portal can request the
data from the OP, again using attribute exchange.
Of course, in this model there is no direct contact between the portal
and grades service in this model, so the portal would need some way of
verifying that the data it got was correct. Digital signatures are
probably the answer here, but there is no standard for this yet (there
was a proposal for this a while back though).
This doesn't look like it would fit our model. Some of the services are
purely RESTful or SOAP (and are currently designed to take CAS proxy
tickets, which seem similar to OAuth...)
2. Use OAuth. The portal acquires an access token to the grades
service. This involves sending the user to the grades service to
authenticate (which might be done using OpenID). The portal can then
use the access token to request the data directly from the grades
service.
This seems like a more viable solution. This is probably more of a OAuth
user list question but I figure I'll check here first. It doesn't look like
OAuth does attribute exchange, is that true? Or is there an extension we
could use (or a standard way to add extensions). My guess is that would
start to get a little weird because if there's no interaction then there is
no way for a user to approve/deny attribute exchanges unless there's a
central decision made about attribute releases (which may work for us, but
probably doesn't work in a general case)
Some of the other stuff is more related to local SSO needs than the
actual
protocol, but I'll ask anyway:
1. Do you support a method of determining whether someone has
authenticated
already (in CAS we call it gateway)? For us it relies on the fact that
you
always point to one CAS server, which obviously doesn't need to be true
in
the case of OpenId.However, in the scenario where you know there is
only
one authenticating server, is this possible?
If you are implementing a closed single sign-on system, you can do the
following:
1. Make the OpenID provider implement an identifier select endpoint.
2. Make the OpenID provider automatically authenticate users who have
already authenticated (perhaps just to known sites).
3. For the relying party sites, if the user is unknown (according to
local session cookie), begin an OpenID authentication request to the
identifier select endpoint. The result will include the user's
identity.
The system we're building would most likely include SSO, so most of this
would already happen. The additional thing CAS offers is that we won't
force you to authenticate if you haven't already, but we will take advantage
of the fact that you have if you did already (i.e. for a portal, if you
haven't authenticated we'll just show a guest layout, but if you have, we'll
actually display your layout). My guess is we'll probably have to propose
our own extension for this.
If you are designing an open system (user can use whatever provider
they want), I don't think there is an answer to this (which provider
are you asking whether the user is authenticated to?).
We're actually considering developing a two-tier system. Locally, we'll
still be interested in using OpenId, but we'd probably point all of our
local apps to a central server. Then our central server would be able to
handle local users or delegate out to other OpenId servers.
2. Similar to above, we support a concept of opting-out and forcing
re-authentication. So an application that contains SSNs may basically
tell
the authentication server, I don't care if they've authenticated already,
do
it again.
The PAPE extension would be appropriate here:
http://openid.net/specs/openid-provider-authentication-policy-extension-1_0-02.html
A relying party site can ask the OP to reauthenticate the user if they
were previously authenticated more than N seconds ago (N can be zero).
Of course, there is nothing to prevent an OP from lying about
reauthenticating the user. If that matters to you, then only accept
OpenID providers you trust.
The last question: We don't actually do this in CAS yet, but we've seen
it
and a few people have asked for it. Is there a way to pass information
along
