Re: [OAUTH-WG] Last Call: <draft-ietf-oauth-jwt-introspection-response-09.txt> (JWT Response for OAuth Token Introspection) to Proposed Standard

> On 31 Aug 2020, at 18:41, Jeff Craig <jeffcraig@google.com> wrote:
> 
> 
> I think that the argument is that token refreshing isn't as strong a signal about usage patterns as introspection calls would be, which I agree with.

It’s usually pretty similar in my experience (see below).  

> I also think that if a RS knows it's using an external AS, they've generally accepted this information leakage. This is not to say it's not worth mentioning in the document, but rather that I doubt it will significantly move implementations one way or the other.

Right. 

> 
> Generally speaking, I don't like JWTs as Access Tokens. They're verbose, they leak information to clients that clients don't need, and if the RS makes a mistake in their JWT validation, they can create security vulnerabilities.  That said, I do think they are preferable to Introspection at request time, and the RS's that I've worked with generally don't want the overhead of Introspection on every usage of the token.

Generally you’d cache the result of the introspection call to mitigate this overhead. (Eg some reverse proxies or API gateways can do this). The two approaches are pretty similar: either you have 10 second access tokens and refresh, or you introspect and cache the response for 10 seconds. 

I much prefer introspection because there are far fewer ways to mess it up, but the JWT approach can be useful if you have clients accessing a lot of different RSes. 

> I generally argue a shared secret between the RS and the AS is a better solution, but in my experience most cloud-hosted ASes don't offer that option.
> 
> For this cloud AS situation, I have been tracking draft-ietf-oauth-token-exchange-19 as a means for RSes to setup a Token Endpoint to convert the AS access token into a access token (w/o Refresh) that the RS can accept, thus limiting Introspection to the Refresh flow, but I don't currently have a RS interested in trying to try this flow, but I think that it's a reasonable approach to limiting introspection on every request to the RS, though it does add an additional point of failure during the Token Refresh. This has the same leakage problem that is under discussion here, obviously.
> 
>> On Mon, Aug 31, 2020 at 3:34 AM Neil Madden <neil.madden@forgerock.com> wrote:
>> But if you want to handle revocation (and you do), then the alternative is short-lived access tokens with frequent refreshing, which also informs the AS of activity. So is this any better?
>> 
>> If an org running an RS decides to use a 3rd-party AS (eg cloud hosted) then there are privacy implications to that arrangement, regardless of the specific technology used for token validation.
>> 
>>>> On 26 Aug 2020, at 22:16, Mike Jones <Michael.Jones=40microsoft.com@dmarc.ietf.org> wrote:
>>>> 
>>> 
>>> I agree with Dick’s observation about the privacy implications of using an Introspection Endpoint.  That’s why it’s preferable to not use one at all and instead directly have the Resource understand the Access Token.  One way of doing this is the JWT Access Token spec.  There are plenty of others.
>>> 
>>>  
>>> 
>>> The downsides of using an Introspection Endpoint should be described in the Privacy Considerations section.
>>> 
>>>  
>>> 
>>>                                                        -- Mike
>>> 
>>>  
>>> 
>>> From: OAuth <oauth-bounces@ietf.org> On Behalf Of Dick Hardt
>>> Sent: Wednesday, August 26, 2020 9:52 AM
>>> To: Torsten Lodderstedt <torsten=40lodderstedt.net@dmarc.ietf.org>
>>> Cc: last-call@ietf.org; oauth <oauth@ietf.org>
>>> Subject: Re: [OAUTH-WG] Last Call: <draft-ietf-oauth-jwt-introspection-response-09.txt> (JWT Response for OAuth Token Introspection) to Proposed Standard
>>> 
>>>  
>>> 
>>>  
>>> 
>>>  
>>> 
>>> On Wed, Aug 26, 2020 at 4:37 AM Torsten Lodderstedt <torsten=40lodderstedt.net@dmarc.ietf.org> wrote:
>>> 
>>> Hi Denis,
>>> 
>>> > On 25. Aug 2020, at 16:55, Denis <denis.ietf@free.fr> wrote:
>>> 
>>> > The fact that the AS will know exactly when the introspection call has been made and thus be able to make sure which client 
>>> > has attempted perform an access to that RS and at which instant of time. The use of this call allows an AS to track where and when 
>>> > its clients have indeed presented an issued access token.
>>> 
>>> That is a fact. I don’t think it is an issue per se. Please explain the privacy implications.
>>> 
>>>  
>>> 
>>> As I see it, the privacy implication is that the AS knows when the client (and potentially the user) is accessing the RS, which is also an indication of when the user is using the client.
>>> 
>>>  
>>> 
>>> I think including this implication would be important to have in a Privacy Considerations section.
>>> 
>>>  
>>> 
>>> /Dick
>>> 
>>> ᐧ
>>> 
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