Re: [OAUTH-WG] PAR and client metadata

Filip Skokan <> Thu, 16 April 2020 08:15 UTC

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From: Filip Skokan <>
Date: Thu, 16 Apr 2020 10:15:17 +0200
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To: Brian Campbell <>
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Subject: Re: [OAUTH-WG] PAR and client metadata
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I would support defining a client level property. I would also support an
AS discovery property for an AS-wide policy that is signalled to all
clients (and maybe that one would be enough).

FWIW (and this touches my earlier responses about the dpop scheme) defining
metadata (both AS and Client) is beneficial not only for runtime (DCR,
discovery) but in general supports developers using these specs, when they
read about a possible behaviour in the document and there's a mentioned
metadata property, they know what to look for in readmes, API
documentation, UI etc. It saves time, theirs, and mine when i develop those
behaviour toggles - i don't have to start mixing configuration objects so
far composed entirely of IANA registered properties with proprietary ones,
i don't need to come up with property names (and we know what a PITA that
is) and it also saves time in the long run because it's less likely someone
will open an issue about it.


On Tue, 14 Apr 2020 at 22:09, Brian Campbell <bcampbell=> 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
> 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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