I may have misunderstood, but I don't think with UMA there is anyway to say a client can only ask for scopes within this "set". (referencing your last paragraph).

Because of the dynamic nature of scopes and permissions tickets, a key capability of a client within UMA is the ability to get access to a resource that requires a scope the client has never even "seen" before. The key to be able to get authorized for this new scope is the ability to mean the ROPolicy for the requested resource. If the client/RqP can meet the required policy, then the RPT is granted the associated scope(s).

I can envision an AS defining a "black list" of scopes that a particular client could NEVER be authorized for, but this seems AS specific and out of scope for UMA.

Thanks,
George

On Mon, Jan 9, 2017 at 4:06 AM James Phillpotts <james.phillpotts@forgerock.com> wrote:

This seems well thought out, thanks Justin. I've got just one concern:

I'm uneasy about using the client registered scopes as 'default scopes' in the case of UMA, when RFC7591 states that registered scopes represent "scope values that the client can use when requesting access tokens" - as you stated in Thursday's call. I'm particularly concerned about how any of this plays out when the client is trying to be both a vanilla OAuth (or OpenID Connect) client as well as an UMA client. If the client registers for scopes "openid profile view edit", then they must explicitly request openid and profile scope values in the token request in order to get an access token that contains those scopes, but if they present a permission ticket as well, we're saying they view and edit will automatically get evaluated/added without the client knowing about it.

I would prefer that we submit an extra 'default_scope' attribute to the OAuth Dynamic Client Registration Metadata Registry (https://tools.ietf.org/html/rfc7591#section-4) to disambiguate from the existing 'scope' field. The client could then register with scope "openid profile edit" and default_scope of "view".

This also has an extra advantage of being able to use the registered scope field to block requests for scope values that have not been registered for the client - i.e. client registers for scope A, has a permission ticket for scope B, but requests scope C in the token request, which should then result in an 'invalid_scope' response.

Cheers
James

On 8 January 2017 at 21:05, Justin Richer <jricher@mit.edu> wrote:

Per the first point: But the AS still has to deal with its own internal processing of "which scopes the RO said were OK if the RqP did certain things good enough" which might not be the same set of scopes requested. This is effectively the set of scopes that result from processing the set of claims supplied by the RqP and client. We *have* to include this in the calculation even though the details of how that's specified by the RO or how the processing engine translates claims to scopes is out of band for us since the *results* of that calculation are bound to show up somehow. And it remains to me to be a clearly limiting set.

Per the second point: It's a separate question whether to reissue the old RPT or reuse its value. No matter what happens there, the question is: what do we do with the scopes associated with the *input* RPT if present? I say we *allow* the AS to add them to the resulting RPT (whether it's now or reissued or whatever, we don't care) but don't *require* the AS to do that. So my pseudocode below is valid but not strictly required as a template for implementors.

Per the third point: the scopes here are nearly all already associated with a resource, apart from ClientReg which tends to be generic in implementations I've seen to date. Namely:
RSTicket - ticket is associated with a specific resource set ID on ticket request

ROPolicy - policy is associated with a specific resource set ID on creation at AS

ClientReq - these are submitted along with a ticket which is associated with a specific resource set ID

RSReg - these are associated with a specific resource set by tautological definition :)

This leaves us two:
        ClientReg - these would tend to be generic, crossing resource sets (likely pertaining to a specific kind of API the client knows how to deal with and not an instance of the same)
        PrevRPT - these might cross a bunch of different resource sets, but at this point the internal permissions structure might be such that they're associated with the token in a way that doesn't overlap the new ones.

To wit, a token starts with:

    rsid_1: { foo, bar }, rsid_2: { baz, qux }

And a new request in the context of rsid_3 adds in { foo, batman } and we end up with:

    rsid_1: { foo, bar }, rsid_2: { baz, qux }, rsid_3: { foo, batman }

That's pretty clearly new stuff. The real trick comes when you get a new request with that first token in the context of rsid_1 again with { foo, batman } being requested/approved. This is the "token step up" function that's been in UMA since forever, and I argue that this *could* come out with a token looking like:

    rsid_1: { foo, bar, batman }, rsid_2: { baz, qux }

Or it *could* come out with a token that looks like:

    rsid_1: { foo, batman }

And it's up to the AS to figure out which it wants to do. Again, note: Whether this permissions set is associated with the same token value string as the input RPT is subject to the logic in your message repeated below, and that's a separate question entirely and ought to be decided orthogonally.

-- Justin

On 1/8/2017 1:51 AM, Eve Maler wrote:

Humongously useful, thank you! Comments on three parts:

====

Policy conditions are out of scope for UMA, so the AS could be configured with all kinds of stuff that is out of scope for what UMA cares about, but since "the AS only knows what the RS told it" as far as UMA goes, RSReg definitely counts as a reasonable limiting factor in my book.

====

Regarding the question of whether the AS honors previous RPTs (K, L): I suspect this is a bit more complex, partially because any RPT could cover more than one resource already, so L is a possibility at any time. The "previous RPT" case would happen when the client chooses to bring a failed RPT to the token endpoint and asks for an RPT that won't fail. The AS has a choice too (as I put it in a recent message):

(Client can bring no RPT and ask for one -- not a concern)

(AS can issue a new RPT A -- not a concern)

Client can bring RPT A that doesn't have a permission for what it wants to do and ask for an RPT that works for what it wants to do

AS is allowed to reissue the existing RPT A (same RPT string), having added the relevant permissions to it

AS can issue a new RPT B (different RPT string), having added the relevant permissions to it

AS can invalidate the old RPT A that the client brought it upon this action

AS can retain the validity of the old RPT A that the client brought it and any of its permission(s) -- presumably ones that are still good and that the client didn't just try to exercise but found wanting

(Justin, you suggested that if the AS issues a new token, we say "the AS SHOULD revoke the existing RPT, if possible" and "the client MUST discard its previous RPT" on the reasoning that this matches OAuth refresh token guidance, which I like.)

You can see I was presuming that reissuing an existing RPT would upgrade that token. If it contained totally orthogonal resources and scopes relative to the current request, it could still be upgraded with a relevant resource and scope.

Is it also possible that the AS's TTL strategy and/or the RO's other changes in policy might also dictate "cleaning house", so to speak, and downgrading other permissions while it's upgrading the permission of interest? Or is this not fair game?

====

Regarding the pièce de résistance (French, meaning "piece of resistance"), the pseudocode, it seems to be pretty complete and logical, and I like that it preserves George's rationale of client registration as a round-trip-saving exercise. The only thing I can't find in it (and this whole discussion, really) is some statement of how scopes match to resources, given that identical scopes may appear on multiple resources. I'm hoping that doesn't have to have to be so much a complication as a matching strategy.

Eve Maler
Cell +1 425.345.6756 | Skype: xmlgrrl | Twitter: @xmlgrrl

On Fri, Jan 6, 2017 at 2:56 PM, Justin Richer <jricher@mit.edu> wrote:

I’ve been working on the set math problem and I’ve been trying to lay out scenarios using this spreadsheet to help me sort my thoughts:

I’ve left a bit of space in the spreadsheet for additional combinations and use cases I might have missed, so please chime in and we can figure out an algorithm that we can all agree on. I can send out the .xlsx file if people care to play with it at home.

So we’ve got six sets of scopes to deal with here, and they’re somewhat independent of each other.

ClientReg - client registers for these scopes at the RS

RSTicket - RS requests a ticket with these scopes

ROPolicy - RO sets a policy with these scopes (and it’s fulfilled by the RqP for our purposes)

ClientReq - client requests these scopes at the token endpoint

RSReg - RS registers these scopes at RS setup time

PrevRPT - client presents a previously-held RPT that’s got some other scopes on it and it’s trying to augment that with new scopes

And finally what the token includes:

RPTResult - the sets that the resulting token includes on output

The one direct relationship seems to be that:

ROPolicy = subset(RSReg)

Because otherwise the RO could set scopes on a resource that the resource didn’t register, which doesn’t make sense to me. That’s the error in column “F” above.

It’s clear to me that “ROPolicy” is a limiting set, in that if a scope is NOT in that set, then it is not in the result. In other words:

RPTResult = subset(ROPolicy)

That’s column D, and nearly any other combination without ROPolicy doesn’t let the scope go through, with one exception: if it’s in PrevRPT, it gets carried through no matter what. But in particular, that, I believe, is an AS decision on whether it wants to honor previous RPTs at all. That’s why I’ve coded those K, L in green.

This also means that RSReg is also a limiting set, due to transitive subset operations:

RPTResult = subset(RSReg)

We have both the client and RS request scopes for the token at runtime in their parts, and it makes a lot of sense to combine them. So we get a working set of:

Requested = union(ClientReq, RSTicket)

We have an open question with what to do with column I: if a client hasn’t requested a scope, and a ticket didn’t request a scope, but the client registered for a scope, do we include it or not? We could choose to either ignore it and leave it out entirely; or add it in, and if it passes ROPolicy then we’ll pass it through to the token. These were the options we were discussing on the call on Thursday. Ignoring it here would effectively ignore the client’s registered scopes entirely, which is valid. The alternative would be coded something like:

Requested = union(ClientReg, ClientReq, RSTicket)

This could also be done conditionally, like the case where the client didn’t specifically request anything:

if (empty(ClientReq)) {

Requested = union(ClientReg, RSTicket)

}

Or if the client or ticket didn’t request anything:

if (empty(ClientReq) && empty(RSTicket)) {

Requested = ClientReg

}

So my proposed implementation would be something like this horrible pseudocode:

if (ROPolicy is not subset(RSReg)) {

throw error and fail <<sanity check>>

}

<< the requested set is made up of the client’s request to the token endpoint and the RS’s request during the ticket issuance step>>

Requested = union(ClientReq, RSTicket)

<< if nothing’s been requested, maybe the client’s registered for something we can default to >>

if (empty(Requested)) {

Requested = ClientReg

}

<< finally, we take the requested scopes and filter out anything not in a matched policy, and add in anything from a previous RPT if it’s there >>

RPTResult = union(

intersection(Requested, ROPolicy),

PrevRPT)

I’ve tested a little bit of this with the following python truth table code:

from truths import Truths

print Truths(['ClientReg', 'RSTicket', 'ROPolicy', 'ClientReq', 'RSReg', 'PrevRPT'], ['(((ClientReq or RSTicket) if not (ClientReq or RSTicket) else ClientReg) and ROPolicy) or PrevRPT'])

This seems to match up to expectations on a quick inspection, but I’m potentially missing something.

Hopefully this makes sense, and this reflects my current thinking on this topic. I have almost certainly missed some use cases and might have some cases that don’t reflect reality.

— Justin

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