Re: [OAUTH-WG] WGLC for Step-up Authentication

[Jaimandeep Singh <[e-mail]>]

Dear Vittorio Bertocci, Brian Campbell and Rifaat,


My sincere compliments to Vittorio and Brian for their persistent efforts
in making and improving the draft RFC and also for taking out valuable time
and efforts to reply to any queries. However, I strongly feel that the
following points should be addressed before closing the last call.

Item No 1: Striking at the core of OAuth 2.0 idea by coupling end user
authentication with authorization.

Explanation: OAuth 2.0 is an authorization protocol. Its strength lies in
the decoupling of the end user authentication with the authorization layer.
The proposed draft proposes means of coupling the two by passage of
authentication information down the complete OAuth 2.0 chain and then
RECOMMENDS actions by AS based on this information, thereby striking at the
core idea of OAuth 2.0.



The idea of end user authentication information being transferred to the AS
is borrowed from OIDC, which sends this information through token ID in the
form of JWT (Refer Section 2 of OIDC specs). This parameter is designed to
be OPTIONAL in OIDC and is not further passed in the access tokens. In the
draft RFC we are not only passing the authentication information down the
chain through access tokens but also acting on the information received
from client applications upstream.



The idea of fiddling with end user authentication is completely foreign to
the OAuth 2.0 specs. Following questions then arise:

   1.

   Do we intend to extend the scope of OAuth 2.0 specs by coupling it with
   the end-user authentication and striking at the very core idea of OAuth
   2.0?
   2.

   OAuth 2.0 does require means of identification for the client
   application either through client ID only in case of public clients or
   through basic authentication in case of confidential clients. Is it not
   better to look at step-up identification/authentication requirements of the
   client application i.e. the way the client application
   identifies/authenticates itself with the AS instead of getting involved
   with the mechanics of end user authentication. The idea of client
   application authentication is intrinsic to the OAuth 2.0 specs.


Item No 2: Punching a security hole by requiring AS to act on information
provided by the client applications (Reverse Flow).

Explanation. Refer Section 4 of draft RFC

The example request below, which might occur after receiving the challenge
> in Figure 2, indicates to the authorization server that the client would
> like the authentication to occur according to the authentication context
> class reference identified by myACR.


> GET https://as.example.net/authorize?client_id=s6BhdRkqt3
> &response_type=code&scope=purchase&acr_values=myACR
> Figure 4: Authorization Request indicating acr_values


In OAuth 2.0 specs, the client application authenticates itself with the AS
before starting the flow. Here, in the example above there are two
prominent flaws:

   1.

   The unauthenticated rogue client makes a GET request to the AS forcing
   the complete authentication breakdown at the end user forcing him to
   authenticate time over and again.
   2.

   Even if we take a scenario that the request is made by an authenticated
   client, the original specs of OAuth 2.0 does not mandate any action based
   on the commands received from the client application. In a zero trust model
   we assume that the client is compromised. AS acting on commands of client
   applications and propagating them across the ecosystem to force the end
   user authentication may result in future unseen vulnerabilities.


Item No 3: Forcing AS to implement OIDC specifications will render existing
implementations non-compliant.

Explanation. Refer Section 5 of the draft specs.

Although [OIDC] leaves the authorization server free to decide how to
> handle the inclusion of acr in ID Token when requested via acr_values, when
> it comes to access tokens in this specification it is RECOMMENDED that the
> requested acr value is treated as required for successfully fulfilling the
> request.


The *RECOMMENDED *and *required* “acr_values” in the access tokens will
render existing deployments of AS, which currently do not support OIDC, as
non-compliant.

Item No 4: How much “Freshness” is fresh?

Explanation. The use of the word “Freshness” is not quantified and does not
convey any meaning. It is recommended to be removed altogether. On the
contrary it complicates the draft, making the reader assume that
“freshness” of authentication is very important and might impact on the
whole idea of access tokens and the OAuth 2.0 in the first place.


On Tue, Oct 18, 2022 at 1:25 AM Brian Campbell <bcampbell=
[e-mail]> wrote:

> Thanks Jaimandeep,
>
> There are certainly some complementary aspects of the step-up work and
> adaptive risk based approaches. Both in conveying information in/with an
> access token that might be input into a risk score calculation and in
> signaling that a more recent and/or stronger user authentication
> is required when the calculated risk exceeds the allowed risk.
>
> On Sat, Oct 15, 2022 at 10:58 PM Jaimandeep Singh <jaimandeep.phdcs21=
> [e-mail]> wrote:
>
>> Dear Brian,
>>
>> I strongly support this work. I have recently written a conference paper
>> on supporting similar ideas titled '*Resilient Risk based Adaptive
>> Authentication and Authorization (RAD-AA) Framework*'. The paper is
>> still in the pre-print stage and can be accessed here
>> <https://arxiv.org/abs/2208.02592>.
>>
>> 1. The core idea is similar. Firstly, ability to revoke or step-up the
>> authentication requirements based on the risk score. Secondly, to limit the
>> scope based on the risk score.
>>
>> 2. One of the factors determining the risk score is the way the client
>> application has authenticated with the Authorization server. If it has used
>> basic auth the risk score is high as compared to mTLS.
>>
>> 3. Additionally the idea is to downgrade the scope of the token in case
>> the risk score is high. This could be achieved at the protected resource
>> server end through introspection and at authorization server end while
>> issuing new access when the older ones expire. This can avoid forcing the
>> complete authentication cycle at client end.
>>
>> Regards
>> Jaimandeep Singh
>>
>>
>> On Wed, Oct 12, 2022 at 3:25 AM Brian Campbell <bcampbell=
>> [e-mail]> wrote:
>>
>>> I don't know offhand a better place or if your specific privacy
>>> consideration is already covered. Honestly, with that comment, I was just
>>> aiming to keep the scope of this document concise and relevant.
>>>
>>> On Tue, Oct 11, 2022 at 10:06 AM Denis <[e-mail]> wrote:
>>>
>>>> Hi Brian,
>>>>
>>>> I agree with you that "must not" is more appropriate in that context.
>>>>
>>>> I also agree with you that the "privacy implications of opaque tokens
>>>> are inherent to OAuth in general".
>>>> However, I have not reviewed all the RFCs and I wonder whether such a
>>>> privacy consideration has already been mentioned.
>>>>
>>>> It would be nice to start to mention it, rather than to continue to
>>>> omit it. Do you see a better place to mention it ?
>>>>
>>>> Denis
>>>>
>>>> Thanks Denis, I agree the word "cannot" isn't quite right there. I
>>>> struggled with trying to find the right wording (more than I probably
>>>> should have) attempting to add a note/reminder without getting into
>>>> normative sounding language. But I also wanted to make a firm statement.
>>>> Words are hard sometimes. Oftentimes! But reading it again today, "cannot"
>>>> doesn't work very well. I think changing to "must not" is appropriate. The
>>>> privacy implications of opaque tokens are inherent to OAuth in general and
>>>> I don't believe this draft is an appropriate place to attempt to give them
>>>> treatment.
>>>>
>>>> On Tue, Oct 11, 2022 at 2:57 AM Denis <[e-mail]> wrote:
>>>>
>>>>> Hi Brian,
>>>>>
>>>>> The text states:
>>>>>
>>>>> Also recall that OAuth 2.0 [RFC6749] assumes access tokens are treated
>>>>> as
>>>>> opaque by clients. So, during the course of any token caching
>>>>> strategy, a client *cannot* inspect the content of the access token to
>>>>> determine the associated authentication information or other details.
>>>>> The token format might be unreadable to the client or might change at
>>>>> any time to become unreadable.
>>>>>
>>>>> A client *can *inspect the content of the access token.
>>>>>
>>>>> A better wording  would be:
>>>>>
>>>>> ...  a client *should not *inspect the content of the access token ...
>>>>>
>>>>> It would be worthwhile to add a Privacy Considerations section:
>>>>>
>>>>> 10. Privacy Considerations
>>>>>
>>>>> Since access tokens are presumed to be opaque to clients, clients (and
>>>>> hence users) are not supposed to inspect the content of the access tokens.
>>>>> Authorizations Servers are able to disclose more information than
>>>>> strictly necessary about the authenticated user without the end user being
>>>>> able to know it. Such additional information may endanger the privacy
>>>>> of the user.
>>>>>
>>>>> Denis
>>>>>
>>>>>
>>>>> I've published an -04. It has that very minor change. There was also
>>>>> an off-list discussion during WGLC that resulted in thinking it'd be
>>>>> worthwhile
>>>>> *to add a reminder that access tokens are opaque to clients*. So I
>>>>> took that as LC feedback and -04 adds a brief note towards that end.
>>>>>
>>>>>
>>>>> https://datatracker.ietf.org/doc/draft-ietf-oauth-step-up-authn-challenge/
>>>>>
>>>>>
>>>>>
>>>>> On Mon, Oct 10, 2022 at 1:22 PM Vittorio Bertocci <vittorio=
>>>>> [e-mail]> wrote:
>>>>>
>>>>>> Thanks Dima for the comment. Some thoughts:
>>>>>>
>>>>>> > (editorial)...
>>>>>> Good point. "statically" would characterize the simplest of the
>>>>>> scenarios, but in fact any case where the AS is the only arbiter of the
>>>>>> authn level works for the point we are trying to make. We'll drop
>>>>>> "statically". Thanks!
>>>>>>
>>>>>> > Apart from...
>>>>>> This spec focuses on empowering an RS to communicate its ACR and
>>>>>> freshness requirements, regardless of the reasons leading the RS to make
>>>>>> that determination: the logic by which that happens is explicitly out of
>>>>>> scope, and in many real life cases it might simply be unknowable (eg
>>>>>> anomaly detection engines based on ML are often back boxes). The mechanism
>>>>>> described here can be used alongside other mechanisms that might require
>>>>>> the client to get the user to interact with the AS, as it is the case for
>>>>>> insufficient_scope, but those remain distinct cases (eg insufficient _scope
>>>>>> might not require any step up but simply explicit user consent, and if it
>>>>>> does require a stepup, that's entirely determined by the AS without any
>>>>>> communication with client or RS required).
>>>>>>
>>>>>> On Fri, Oct 7, 2022 at 17:43 Dima Postnikov <[e-mail]>
>>>>>> wrote:
>>>>>>
>>>>>>> *This message originated outside your organization.*
>>>>>>>
>>>>>>> ------------------------------
>>>>>>>
>>>>>>> Couple of quick comments from me:
>>>>>>>
>>>>>>> 1) (Editorial) >In simple API authorization scenarios, an
>>>>>>> authorization server will statically determine what authentication technique
>>>>>>>
>>>>>>> In many scenarios, authorization servers will use *dynamic*
>>>>>>> decisioning to determine authentication techniques; it's just not
>>>>>>> exposed to the client in a way to make it actionable (which is why this
>>>>>>> specification's intent makes perfect sense).
>>>>>>>
>>>>>>> 2) Apart from authentication level, there might be other reasons why
>>>>>>> users might be forced to go through the authorization flow, for example,
>>>>>>> insufficient authorization / scopes / claims / etc.
>>>>>>>
>>>>>>> If there is a mechanism to let the client know, as a practitioner,
>>>>>>> i'd rather have the same approach for both authentication and
>>>>>>> authorization. There are a range of authorization policy engines in the
>>>>>>> market that could return "STEP UP is required" after looking at
>>>>>>> authentication, authorisation and many other real-time signals. It's just
>>>>>>> not standardized...
>>>>>>>
>>>>>>>
>>>>>>> On Sat, Oct 8, 2022 at 7:30 AM Pieter Kasselman <pieter.kasselman=
>>>>>>> [e-mail]> wrote:
>>>>>>>
>>>>>>>> I am very supportive of this work and have been working through
>>>>>>>> different use cases to see whether it can satisfy the requirements that
>>>>>>>> arise from them.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> One observation from working through these uses cases is that as
>>>>>>>> customers move to Zero Trust architectures, we are seeing customers
>>>>>>>> adopting finer grained policy segmentation. Consequently customers are
>>>>>>>> planning to deploy segmented access control by data or action sensitivity,
>>>>>>>> within a service. This approach to policy design makes it more common for a
>>>>>>>> single service to depend on multiple authentication context values or
>>>>>>>> combinations of authentication context values.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> An example of this is a policy that has multiple acr values (e.g.
>>>>>>>> acr1=password, acr2=FIDO, acr3=selfie check, acr4=trusted network). A
>>>>>>>> customer may define a policy that requires different combinations of these
>>>>>>>> acr values, for example, a file server may requires password for general
>>>>>>>> access (e.g. acr1), FIDO authentication (acr2) or password access and being
>>>>>>>> on a trusted network to read sensitive data (acr 2 of (acr1 + acr 4), FIDO
>>>>>>>> authentication and password (acr1 + acr2) for accessing editing sensitive
>>>>>>>> documents and a real-time selfie check on top of FIDO and presence on a
>>>>>>>> trusted network  (acr1 + acr2 + acr3 + acr4) to initiate a sensitive
>>>>>>>> workflow (e.g. check-in code). Other variations of this includes database
>>>>>>>> access with different types of access requirement for certain rows
>>>>>>>> (row-level permissions) or columns (column level permissions) with
>>>>>>>> different combinations of acr values.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> I was curious if this type of scenario where multiple
>>>>>>>> authentication contexts and combinations of contexts are required is
>>>>>>>> something others see (or are beginning to see) as well?
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Cheers
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Pieter
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> *From:* OAuth <[e-mail]> *On Behalf Of *Rifaat
>>>>>>>> Shekh-Yusef
>>>>>>>> *Sent:* Thursday, September 22, 2022 3:02 PM
>>>>>>>> *To:* oauth <[e-mail]>
>>>>>>>> *Subject:* Re: [OAUTH-WG] WGLC for Step-up Authentication
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> *Correction:*
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Please, review the document and provide your feedback on the
>>>>>>>> mailing list by *Oct 7th, 2022*.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Sep 22, 2022 at 9:52 AM Rifaat Shekh-Yusef <
>>>>>>>> [e-mail]> wrote:
>>>>>>>>
>>>>>>>> All,
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> This is to start a *WG Last Call *for the *Step-up Authentication *
>>>>>>>> document:
>>>>>>>>
>>>>>>>> https://www.ietf.org/archive/id/draft-ietf-oauth-step-up-authn-challenge-03.html
>>>>>>>> <https://urldefense.com/v3/__https://nam06.safelinks.protection.outlook.com/?url=https*3A*2F*2Fwww.ietf.org*2Farchive*2Fid*2Fdraft-ietf-oauth-step-up-authn-challenge-03.html&data=05*7C01*7Cpieter.kasselman*40microsoft.com*7C0078f809101147bc978308da9ca32020*7C72f988bf86f141af91ab2d7cd011db47*7C1*7C0*7C637994521713812011*7CUnknown*7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0*3D*7C3000*7C*7C*7C&sdata=18sfemyWqYb06PvUA9eTLaq0ccDY14*2F6ETo58JpE*2FJQ*3D&reserved=0__;JSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUl!!PwKahg!537tJQfGj3Z_Yi2waywl1VPGyDs9818JE-M-KNFgPtoB0O26a7ksRvAYrPyzfKKXsMKCVblAomtRXj8$>
>>>>>>>>
>>>>>>>>
>>>>>>>> Please, review the document and provide your feedback on the
>>>>>>>> mailing list by *Sep 30th, 2022*.
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>>  Rifaat & Hannes
>>>>>>>>
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>> --
>> Regards and Best Wishes
>> Jaimandeep Singh
>> LinkedIn <http://www.linkedin.com/in/jaimandeep-singh-07834b1b7>
>>
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-- 
Regards and Best Wishes
Jaimandeep Singh
LinkedIn <http://www.linkedin.com/in/jaimandeep-singh-07834b1b7>