Re: [OAUTH-WG] PAR and client metadata

[Brian Campbell <[e-mail]>]

require_pushed_authorization_requests works for me and is maybe/arguably a
bit better by being more consistent with other names.

On Mon, Apr 27, 2020 at 12:58 PM Filip Skokan <[e-mail]> wrote:

> Alternatively, `require_pushed_authorization_requests`. Since we already
> have the `*require_*request_uri_registration` server and `*require_*
> auth_time` client metadata properties.
>
> WDYT?
>
> S pozdravem,
> *Filip Skokan*
>
>
> On Sun, 26 Apr 2020 at 16:58, Torsten Lodderstedt <torsten=
> [e-mail]> wrote:
>
>> Hi all,
>>
>> I think this topic has several aspects:
>> - Is the client required to use PAR only? Doesn’t this also mean it is
>> required to use request_uri only?
>> - Is there a need to separate those to questions or shall we treat this
>> as the same?
>> - Who decides whether PAR and request_uri are required? The client for
>> its instances or the AS for the whole deployment?
>>
>> I’m in favour of coupling enforced PAR use with enforced request_uri use
>> even though it means the setting is useful with PAR only, not with all
>> JAR-based clients.
>> I think both the client as well as the AS should be able to declare
>> forced PAR. If the AS is able to basically turn of traditional
>> authorization requests, it can consequently utilize the changed protocol
>> properties in terms of security and robustness in its deployment. This
>> means, for example, the AS no longer needs to require pre-registered
>> redirect URIs for confidential clients. It also means, the AS can use
>> voluminous claims/authorization details objects without worrying about
>> fragile long request URLs.
>>
>> So here is my proposal:
>>
>> 1) Add server metadata parameter “pushed_authorization_requests_only” of
>> type boolean - It requires any client to use PAR, the AS will refuse to
>> process any authorization request containing parameters other than
>> request_uri + client_id (as required by
>> https://tools.ietf.org/html/draft-ietf-oauth-jwsreq-21). Extension
>> request parameters need to be passed via PAR.
>> 2) Add client registration parameter “pushed_authorization_requests_only”
>> - It requires this client to use PAR only. The AS won’t accept any
>> authorization request containing more than request_uri + client_id for that
>> particular client.
>>
>> What are your thoughts?
>>
>> best regards,
>> Torsten.
>>
>> > On 19. Apr 2020, at 10:09, Vladimir Dzhuvinov <[e-mail]>
>> wrote:
>> >
>> > In a off-list conversation Torsten floated the idea of letting
>> confidential PAR-only clients register without a redirect_uris and having
>> this "PAR only" parameter will enable that.
>> >
>> > A "PAR only" parameter will also prevent client developers from
>> accidentally making plain authz requests (for clients that rely on PAR for
>> the extra security).
>> >
>> > Vladimir
>> >
>> > On 16/04/2020 18:39, Brian Campbell wrote:
>> >>
>> >>
>> >> On Wed, Apr 15, 2020 at 1:44 PM Richard Backman, Annabelle <richanna=
>> [e-mail]> wrote:
>> >> As I think through this, I’m struggling to identify the threats this
>> actually helps mitigate.
>> >>
>> >> A client metadata parameter implies that the value may be different
>> for different clients, and that any given client won’t already know via
>> other means whether or not it needs to use PAR. That means we’re only
>> talking about dynamic clients since statically registered clients already
>> have some proprietary out-of-band registration mechanism (e.g., a developer
>> console).
>> >>
>> >> As I tried to articulate in the original email and Filip also
>> mentioned in a different fork of this email thread, defining metadata can
>> be beneficial even when it's not used dynamically at runtime. So we're not
>> only talking about dynamic clients.
>> >>
>> >>
>> >>
>> >> A client metadata parameter also implies that the AS allows some
>> clients to make non-PAR requests (otherwise it would be an AS metadata
>> parameter).
>> >>
>> >> A per client setting seems necessary for existing ASs to roll out PAR
>> support over time or just generally in support of diverse client
>> capabilities and requirements.
>> >>
>> >>
>> >> If that’s the case then presumably a malicious party could register
>> their own client that doesn’t use PAR.
>> >>
>> >> So it seems to me that the only scenario that this parameter would
>> protect against is a malicious party impersonating a dynamically registered
>> client that uses PAR. That wouldn’t apply to Mix-Up, since in that attack
>> the attacker uses its own client.
>> >>
>> >> This client metadata parameter is meant to be something that would
>> prevent a malicious actor from controlling the content of the authz request
>> parameters, which could be done by crafting the link and tricking a user
>> into following it. I mentioned mix-up as an example because the first
>> variant of it desribed at
>> https://tools.ietf.org/html/draft-ietf-oauth-security-topics-15#section-4.4.1
>> does something along those lines.
>> >>
>> >>
>> >>
>> >> If a client can do PAR, then it can do authorization code grant and
>> PKCE, so we’re further limited to scenarios where the attacker does not
>> need to be able to redeem the authorization code themselves. What threats
>> fall into this category?
>> >>
>> >> —
>> >> Annabelle Backman (she/her)
>> >> AWS Identity
>> >>
>> >>> On Apr 14, 2020, at 2:44 PM, Brian Campbell <bcampbell=
>> [e-mail]> wrote:
>> >>>
>> >>> 
>> >>> CAUTION: This email originated from outside of the organization. Do
>> not click links or open attachments unless you can confirm the sender and
>> know the content is safe.
>> >>>
>> >>>
>> >>> I was hoping to get to a rough consensus in support of the idea
>> before coming up with a name that everyone will hate :)
>> >>>
>> >>> In the meantime, however, name suggestions are of course welcome.
>> >>>
>> >>>
>> >>> On Tue, Apr 14, 2020 at 2:22 PM Vladimir Dzhuvinov <
>> [e-mail]> wrote:
>> >>> I'm all for that.
>> >>>
>> >>> I suppose you have already thought of a suitable name? :)
>> >>>
>> >>> Vladimir
>> >>>
>> >>> On 14/04/2020 23:08, Brian Campbell wrote:
>> >>>> Using PAR can facilitate improved security by giving clients a
>> (relatively) simple means for sending a confidential, integrity protected,
>> and (for confidential clients anyway) authenticated authorization request.
>> >>>>
>> >>>> It seems like some of that improved security could be undermined by
>> a malicious actor somehow getting a user to navigate to a URL of a regular
>> old parameterized authorization request. One variation of the Mix-Up Attack
>> does this
>> https://tools.ietf.org/html/draft-ietf-oauth-security-topics-15#section-4.4.1
>> for example and email, social media, online forums, etc., are other ways a
>> user might be tricked into following a maliciously crafted link.
>> >>>>
>> >>>> Following from that it seems logical that an authorization server
>> might want to restrict some clients from sending a regular parameterized
>> authorization request and instead require use of the PAR endpoint to
>> initiate an authorization request. Something like this could, of course, be
>> implemented as custom policy or configuration in any AS. But I'm thinking
>> it might be common enough to warrant adding a client metadata parameter to
>> the PAR draft specifically for it. The metadata (and registered extensions)
>> defined by Dynamic Client Registration [RFC7591] has come to imply a
>> general data model and expected associated behaviors for clients that is
>> useful for authorization server implementations, even when the Dynamic
>> Client Registration Protocol isn't directly in play. This particular
>> situation seems like a good potential candidate for a new such client
>> metadata parameter that would indicate that the given client can only use a
>> request_uri value obtained from the PAR endpoint to initiate an
>> authorization request. And that a regular old fashioned authorization
>> request from the given client would result in an error.
>> >>>>
>> >>>> Do the folks of this fine WG think something like this would be a
>> worthwhile addition to the PAR draft?
>> >>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>>
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