Re: [OAUTH-WG] [Openid-specs-ab] OAuth Security Topics -- Recommend authorization code instead of implicit

[Nat Sakimura <[e-mail]>]

Self Issued OP is described in Chapter 7 of the OpenID Connect Core 1.0.
It lives on a local machine, typically a phone. Even if it did provide an
authorization code to the client, the client cannot establish a direct
connection to the local machine (phone) as it is not addressable.
Therefore, a token endpoint cannot be provided unless it is coupled with
some kind of cloud-based service, which would negate some of the very
reason for having the Self-issued OP. In other words, only the viable
communication channel between the SIOP and the client is the front channel.
The situation could be true to other "wallet" type of implementations.

This is one of the exotic features of OpenID Connect that never got a
traction but it is getting a renewed interest as "Self-sovereign Identity"
gained some interest.



On Wed, Nov 28, 2018 at 6:03 AM Torsten Lodderstedt <[e-mail]>
wrote:

> I still don’t understand why the use case must be solved using a flow
> issuing something in the front channel.
>
> I would also like to take a closer look. Can you or Nat provide pointers
> to existing implementations?
>
> > Am 27.11.2018 um 21:36 schrieb John Bradley <[e-mail]>:
> >
> > I understand that, but hat is Nat's concern as I understand it.
> >
> > When we say no implicit people, have a problem because implicit is
> imprecise.
> >
> > We are saying no AT returned in the response from the authorization
> endpoint.
> >
> > Nat points out that id_token may contain AT for the self issued client.
> >
> > So unless we say that is OK if the AT are sender constrained we wind up
> implying that a OpenID profile of OAuth is in violation of the BCP.
> >
> > I am just trying to make sure everyone is on the same page with why Nat
> was -1.
> >
> > It really has nothing to do with the SPA use case.
> >
> > John B.
> >
> >> On 11/27/2018 5:28 PM, Torsten Lodderstedt wrote:
> >> Hi John,
> >>
> >> as you said, self issued IDPs (
> https://openid.net/specs/openid-connect-core-1_0.html#SelfIssued) are
> supposed to provide the response type „id_token“ only. I don’t think the
> proposal being discussed here is related to this OIDC mode.
> >>
> >> best regards,
> >> Torsten.
> >>
> >>> Am 27.11.2018 um 20:54 schrieb John Bradley <[e-mail]>:
> >>>
> >>> I talked to Nat about this a bit today.
> >>>
> >>> The thing he is concerned about is mostly around the self issued IDP
> that doesn't have a token endpoint(atleast not easaly).
> >>>
> >>> The main use case for that is the id_token response type where claims
> are retuned in the id_token.
> >>>
> >>> Because it is fragment encoded some people call that implicit.   That
> is not what we are trying to stop.
> >>>
> >>> In some cases in that flow there may be distributed claims returned
> with access Token inside the id_token.    I think most people would agree
> that those should be pop or sender constrained tokens.
> >>>
> >>> In the case of self issued the RP would be a server and could do
> sender constrained via some mechinisim that is yet to be defined.
> >>>
> >>> So if someone wanted to return a access token in a id_token to do
> distributed claims I don't think we have a problem with that as long as the
> token is protected by being sender constrained in some reasonable way.
> >>>
> >>> This is a touch hypothetical from the basic OAuth perspective, so I
> don't know how deep we want to go into it.
> >>>
> >>> I think the point is not to accidently prohibit something that could
> be done in future.
> >>>
> >>> I also think we should not conflate confidential clients that can
> authenticate to the token endpoint with sender constrained/PoP clients that
> can deal with bound tokens.   Yes both have keys but it is better to
> describe them separately.
> >>>
> >>> John B.
> >>>
> >>> On Tue, Nov 27, 2018, 4:30 PM Torsten Lodderstedt via Openid-specs-ab <
> [e-mail] wrote:
> >>> Hi Nat,
> >>>
> >>> I understand you are saying your draft could provide clients with an
> application level mechanism to sender constrain access tokens. That’s great!
> >>>
> >>> But I don’t see a binding to response type „token id_token“. Why do
> you want to expose the tokens via the URL to attackers?
> >>>
> >>> You could easily use your mechanism with code. That would also give
> you the chance to really authenticate the confidential client before you
> issue the token.
> >>>
> >>> kind regards,
> >>> Torsten.
> >>>
> >>>> Am 27.11.2018 um 16:57 schrieb Nat Sakimura <[e-mail]>:
> >>>>
> >>>> I am not talking about SPA.
> >>>> The client is a regular confidential client that is running on a
> server.
> >>>>
> >>>> Best,
> >>>>
> >>>> Nat Sakimura
> >>>>
> >>>>
> >>>> 2018年11月27日(火) 16:55 Jim Manico <[e-mail]>:
> >>>> Nat,
> >>>>
> >>>> How is proof of possession established in a modern web browser in the
> implicit flow?
> >>>>
> >>>> My understanding is that token binding was removed from Chrome
> recently effectively killing browser-based PoP tokens.
> >>>>
> >>>>
> https://identiverse.com/2018/10/31/chrome-puts-token-binding-in-a-bind/
> >>>>
> >>>> Am I missing something?
> >>>>
> >>>> Aloha, Jim
> >>>>
> >>>>
> >>>>
> >>>>> On 11/27/18 9:00 PM, Nat Sakimura wrote:
> >>>>> I am actually -1.
> >>>>>
> >>>>> +1 for public client and the tokens that are not sender/key
> constrained.
> >>>>>
> >>>>> Just not being used right now does not mean that it is not useful..
> In fact, I see it coming.
> >>>>> Implicit (well, Hybrid “token id_token” really) is very useful in
> certain cases.
> >>>>> Specifically, when the client is confidential (based on public key
> pair), and uses sender constrained (key-constrained) token such as the one
> explained in
> https://tools.ietf.org/html/draft-sakimura-oauth-jpop-04#section-5, it is
> very useful.
> >>>>> (Key-constrained token is the remaining portion of this draft that
> did not get incorporated in the MTLS draft. )
> >>>>> In fact it is the only viable method for Self-Issued OpenID Provider.
> >>>>>
> >>>>> So, the text is generally good but it needs to be constrained like
> “Unless the client is confidential and the access token issued is key
> constrained, ... “
> >>>>>
> >>>>> Best,
> >>>>>
> >>>>> Nat Sakimura
> >>>>>
> >>>>>
> >>>>> 2018年11月27日(火) 16:01 Vladimir Dzhuvinov <[e-mail]>:
> >>>>> +1 to recommend the deprecation of implicit.
> >>>>>
> >>>>> I don't see a compelling reason to keep implicit when there is an
> >>>>> established alternative that is more secure.
> >>>>>
> >>>>> Our duty as WG is to give developers the best and most sensible
> practice.
> >>>>>
> >>>>> CORS adoption is currently at 94% according to
> >>>>> https://caniuse.com/#feat=cors
> >>>>>
> >>>>> Vladimir
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>> OAuth mailing list
> >>>>> [e-mail]
> >>>>> https://www.ietf.org/mailman/listinfo/oauth
> >>>>> --
> >>>>> Nat Sakimura (=nat)
> >>>>> Chairman, OpenID Foundation
> >>>>> http://nat..sakimura.org/
> >>>>> @_nat_en
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>> OAuth mailing list
> >>>>>
> >>>>> [e-mail]
> >>>>> https://www.ietf.org/mailman/listinfo/oauth
> >>>> --
> >>>> Jim Manico
> >>>> Manicode Security
> >>>>
> >>>> https://www.manicode.com
> >>>> --
> >>>> Nat Sakimura (=nat)
> >>>> Chairman, OpenID Foundation
> >>>> http://nat.sakimura.org/
> >>>> @_nat_en
> >>>> _______________________________________________
> >>>> OAuth mailing list
> >>>> [e-mail]
> >>>> https://www.ietf.org/mailman/listinfo/oauth
> >>> _______________________________________________
> >>> Openid-specs-ab mailing list
> >>> [e-mail]
> >>> http://lists.openid.net/mailman/listinfo/openid-specs-ab
>


-- 
Nat Sakimura (=nat)
Chairman, OpenID Foundation
http://nat.sakimura.org/
@_nat_en