Re: [OAUTH-WG] [UNVERIFIED SENDER] Re: PAR metadata

[Brian Campbell <[e-mail]>]

A little more context about that proposed wording is in a github issue at
https://github.com/oauthstuff/draft-oauth-par/issues/38, which is different
driver than allowing a PAR endpoint to stash the encrypted request object
rather than decrypting/validating it. But it's kind of the same concept at
some level too - that there are some things that can't or won't be
validated at the PAR endpoint and those then have to be validated at the
authorization endpoint.

I rather like your suggested text, Vladimir, and have mentioned it in a
comment on the aforementioned issue.


On Tue, Jan 7, 2020 at 6:58 AM Vladimir Dzhuvinov <[e-mail]>
wrote:

> On 07/01/2020 00:22, Filip Skokan wrote:
>
> We've been discussing making the following change to the language
>
> The AS SHOULD validate the request in the same way as at the authorization
>> endpoint. The AS MUST ensure that all parameters to the authorization
>> request are still valid at the time when the request URI is used.
>>
> Could you expand a bit on the second sentence?
>
> Alternative suggestion:
>
> The AS MUST validate the request in the same way as at the authorization
> endpoint, or complete the request validation at the authorization endpoint.
>
> Vladimir
>
>
> This would allow the PAR endpoint to simply stash the encrypted request
> object instead of decrypting and validating it. All within the bounds of
> "SHOULD - We’d like you to do this, but we can’t always require it". This
> supports "light weight PAR" implementation rather than introducing the
> unnecessary complexity in the form of a second JWKS.
>
> Best,
> *Filip*
>
>
> On Mon, 6 Jan 2020 at 23:00, Richard Backman, Annabelle <richanna=
> [e-mail]> wrote:
>
>> The issue isn’t that the PAR endpoint needs access to one specific
>> request object decryption key that could reasonably be shared across AS
>> endpoints, but that it actually needs access to the private keys for all
>> encryption public keys in the JWK set pointed to by the AS’s jwks_uri
>> metadata property. Since there is no way to designate one particular key as
>> the one to use for encrypting request objects, clients may reasonably use
>> any encryption public key in the JWK set to encrypt a request object. As
>> one example of how this could expose sensitive data to the PAR endpoint, if
>> the PAR endpoint has all the decryption keys for the keys in the AS’s JWK
>> set, it would be able to decrypt ID Tokens sent in id_token_hint request
>> parameters. As more and more use cases develop for encrypting blobs for the
>> AS, this issue will only get worse.
>>
>>
>>
>> The PAR endpoint can’t simply stash the encrypted request object, as it
>> is required to verify the request, according to §2.1:
>>
>>
>>
>> The AS MUST process the request as follows:
>>
>>
>>
>> ...
>>
>>
>>
>> 3.  The AS MUST validate the request in the same way as at the
>>
>>           authorization endpoint. ...
>>
>>
>>
>> This language needs to be more flexible, IMHO, to allow for lightweight
>> PAR endpoints that may not have the information or authority needed to
>> perform all the validation that happens at the authorization endpoint. I
>> need to think about this more before I can say if it would adequately
>> address my concerns, but it’d be a good start and makes sense in its own
>> right.
>>
>>
>>
>> I think it’s pretty risky for us to base decision on an assumption that
>> no one is going to need or want to encrypt pushed request objects,
>> particularly when they’re JWTs, and JWTs have well established support for
>> encryption, and encrypted JWTs are supported by pass-by-value in OIDC and
>> draft-ietf-oauth-jwsreq. But if you insist, here are a few examples for why
>> someone might want to do this:
>>
>>    1. The request object is passed by reference, and accessible on the
>>    public Internet.
>>    2. The request object contains sensitive transaction-related data in
>>    RAR parameters that the client’s authN/authZ stack doesn’t need to have
>>    access to.
>>    3. The AS requires request object encryption to minimize exposure to
>>    the hosted PAR endpoint service it uses.
>>    4. #2, but the threat vector is gaps in end-to-end TLS.
>>    5. Any of the above, but the concern is message integrity, and the AS
>>    requires requested objects to be encrypted for confidentiality and
>>    integrity protection and does not support signed request objects.
>>
>>
>>
>> –
>>
>> Annabelle Richard Backman
>>
>> AWS Identity
>>
>>
>>
>>
>>
>> *From: *Neil Madden <[e-mail]>
>> *Date: *Monday, January 6, 2020 at 6:29 AM
>> *To: *Brian Campbell <[e-mail]>
>> *Cc: *"Richard Backman, Annabelle" <[e-mail]>, Nat Sakimura <
>> [e-mail]>, Dave Tonge <[e-mail]>, Torsten
>> Lodderstedt <torsten@lodderstedt..net <[e-mail]>>, oauth <
>> [e-mail]>
>> *Subject: *[UNVERIFIED SENDER] Re: [OAUTH-WG] PAR metadata
>>
>>
>>
>> Agreed.
>>
>>
>>
>> In addition, I'm not sure why the PAR endpoint would need access to the
>> decryption keys at all. If you're using encrypted request objects then the
>> PAR endpoint receives an encrypted JWT and then later makes the same (still
>> encrypted) JWT available to the authorization endpoint. If the PAR endpoint
>> is doing any kind of decryption or validation on behalf of the
>> authorization endpoint then they are clearly not in separate trust
>> boundaries.
>>
>>
>>
>> -- Neil
>>
>>
>>
>>
>>
>> On 6 Jan 2020, at 13:57, Brian Campbell <
>> bcampbell=[e-mail]> wrote:
>>
>>
>>
>> I really struggle to see the assumption that an entity be able to use the
>> same key to decrypt the same type of message ultimately intended for the
>> same purpose as an artificial limit. The same general assumption
>> underlies everything else in OAuth/OIDC (Vladimir's post points to some but
>> not all examples of such). There's no reason for PAR to make a one-off
>> exception. And should there be some deployment specific reason that truly
>> requires that kind of isolation, there are certainly implementation options
>> that aren't compatibility-breaking. And having said all that, I'm honestly
>> a little surprised anyone is thinking much about encrypted request objects
>> with PAR as, at least with my limited imagination, there's not really a
>> need for it.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Fri, Jan 3, 2020 at 2:43 PM Richard Backman, Annabelle <richanna=
>> [e-mail]> wrote:
>>
>> PAR introduces an added wrinkle for encrypted request objects: the PAR
>> endpoint and authorization endpoint may not have access to the same
>> cryptographic keys, even though they're both part of the "authorization
>> server." Since they're different endpoints with different roles, it's
>> reasonable to put them in separate trust boundaries. There is no way to
>> support this isolation with just a single "jwks_uri" metadata property.
>>
>> The two options that I see are:
>>
>> 1. Define a new par_jwks_uri metadata property.
>> 2. Explicitly state that this separation is not supported.
>>
>> I strongly perfer #1 as it has a very minor impact on deployments that
>> don't care (i.e., they just set par_jwks_uri and jwks_uri to the same
>> value) and failing to support this trust boundary creates an artificial
>> limit on implementation architecture and could lead to
>> compatibility-breaking workarounds.
>>
>> –
>> Annabelle Richard Backman
>> AWS Identity
>>
>>
>> On 12/31/19, 8:07 AM, "OAuth on behalf of Torsten Lodderstedt" <
>> [e-mail] on behalf of torsten=
>> [e-mail]> wrote:
>>
>>     Hi Filip,
>>
>>     > On 31. Dec 2019, at 16:22, Filip Skokan <[e-mail]> wrote:
>>     >
>>     > I don't think we need a *_auth_method_* metadata for every endpoint
>> the client calls directly, none of the new specs defined these (e.g. device
>> authorization endpoint or CIBA), meaning they also didn't follow the scheme
>> from RFC 8414 where introspection and revocation got its own metadata. In
>> most cases the unfortunately named `token_endpoint_auth_method` and its
>> related metadata is what's used by clients for all direct calls anyway.
>>     >
>>     > The same principle could be applied to signing (and encryption)
>> algorithms as well.
>>     >
>>     > This I do not follow, auth methods and their signing is dealt with
>> by using `token_endpoint_auth_methods_supported` and
>> `token_endpoint_auth_signing_alg_values_supported` - there's no encryption
>> for the `_jwt` client auth methods.
>>     > Unless it was meant to address the Request Object signing and
>> encryption metadata, which is defined and IANA registered by OIDC. PAR only
>> references JAR section 6.1 and 6.2 for decryption/signature validation and
>> these do not mention the metadata (e.g. request_object_signing_alg) anymore
>> since draft 07.
>>
>>     Dammed! You are so right. Sorry, I got confused somehow.
>>
>>     >
>>     > PS: I also found this comment related to the same question about
>> auth metadata but for CIBA.
>>
>>     Thanks for sharing.
>>
>>     >
>>     > Best,
>>     > Filip
>>
>>     thanks,
>>     Torsten.
>>
>>     >
>>     >
>>     > On Tue, 31 Dec 2019 at 15:38, Torsten Lodderstedt <
>> [e-mail]> wrote:
>>     > Hi all,
>>     >
>>     > Ronald just sent me an email asking whether we will define metadata
>> for
>>     >
>>     > pushed_authorization_endpoint_auth_methods_supported and
>>     > pushed_authorization_endpoint_auth_signing_alg_values_supported.
>>     >
>>     > The draft right now utilises the existing token endpoint
>> authentication methods so there is basically no need to define another
>> parameter. The same principle could be applied to signing (and encryption)
>> algorithms as well.
>>     >
>>     > What’s your opinion?
>>     >
>>     > best regards,
>>     > Torsten.
>>
>>
>>
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