Re: [OAUTH-WG] Alissa Cooper's Discuss on draft-ietf-oauth-introspection-09: (with DISCUSS and COMMENT)

Justin Richer <jricher@MIT.EDU> Thu, 11 June 2015 21:01 UTC

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From: Justin Richer <jricher@MIT.EDU>
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To: Alissa Cooper <alissa@cooperw.in>
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Subject: Re: [OAUTH-WG] Alissa Cooper's Discuss on draft-ietf-oauth-introspection-09: (with DISCUSS and COMMENT)
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Hi Alissa, thanks for your review. Responses are inline.

> On Jun 8, 2015, at 9:40 AM, Alissa Cooper <alissa@cooperw.in> wrote:
> 
> Alissa Cooper has entered the following ballot position for
> draft-ietf-oauth-introspection-09: Discuss
> 
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> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> for more information about IESG DISCUSS and COMMENT positions.
> 
> 
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-oauth-introspection/
> 
> 
> 
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
> 
> = Section 2.1 =
> "The endpoint MAY allow other parameters to provide further context to
>   the query.  For instance, an authorization service may need to know
>   the IP address of the client accessing the protected resource in
>   order to determine the appropriateness of the token being presented."
> 
> How does the protected resource know whether it needs to include such
> additional parameters or not?
> What is meant by the "appropriateness" of
> the token? 
> 
> In general if we're talking about a piece of data that could be sensitive
> like client IP address, it would be better for there to be specific
> guidelines to direct protected resources as to when this information
> needs to be sent. I note that Section 5 basically says such
> considerations are out of scope, but if this specific example is to be
> provided here then they seem in scope to me.

We are trying to leave the door open to extensions and adaptations of this protocol, specifically around the protected resource passing along information about the client’s request. The AS might be able to help the RS detect funny business on the client’s behalf (i.e., whether it’s appropriate for the client to presenting the token in this context) if it has that information. 

The example isn’t supposed to be normative or pull extra considerations into scope of this protocol but instead to point out where it could go.

Do you have a suggestion for rewording this? Perhaps it would be best to move all of this language to the security considerations section, as it’s more guidance for what extensions to this spec would need to think about as opposed to what pure implementations of this spec would need.

> 
> = Section 5 =
> "One way to limit disclosure is to require
>   authorization to call the introspection endpoint and to limit calls
>   to only registered and trusted protected resource servers."
> 
> I thought Section 2.1 made authorization to call the introspection
> endpoint mandatory. This makes it sound like it's optional. Which is it?

Thanks for this catch. Authorization used to be optional, and it looks like we missed updating this text. I’ll fix that in the next revision.

> 
> 
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> = Section 1.1 =
> There is no reference to RFC2119 here, which may be okay but most
> documents include it if they use normative language (I think).
> 

Not sure how that happened, this should have been included by the xml2rfc tooling, I’ll look into it.

> = Section 2 =
> "The
>   definition of an active token is up to the authorization server, but
>   this is commonly a token that has been issued by this authorization
>   server, is not expired, has not been revoked, and is within the
>   purview of the protected resource making the introspection call."
> 
> Is "within the purview" a term of art for OAuth 2.0? Is there a more
> specific way to describe what is meant here? Also, I note that in the
> description of the "active" member in Section 2.2, this criterion is not
> listed. It seems like these should be aligned.

It is not a term of art in OAuth, and I can change that to “is able to be used at the protected resource” if that’s clearer. I will also add that to the list of checks about the active value, thanks.

> 
> = Section 2.2 =
> "Note that in order to avoid disclosing too much of the
>   authorization server's state to a third party, the authorization
>   server SHOULD NOT include any additional information about an
>   inactive token, including why the token is inactive."
> 
> Seems like this should be a MUST NOT unless there's some reason for
> providing anything other than active set to false. Same comment applies
> in Section 4.

That’s why it’s SHOULD — which translates, roughly, to “do it this way unless you’ve got a really, really good reason not to”.

> 
> = Section 2.3 =
> It seems like there is another error condition and I'm wondering if its
> handling needs to be specified. Per my question in Section 2.1, if it's
> possible that the request is properly formed but is missing some
> additional information that the authorization server needs to evaluate
> it, should there be an error condition specified for that case?
> 

Not by this specification, since there isn’t a mechanism for the protected resource to figure out automatically what to do next. If there’s a future extension specifying this extra information, it can define its own value.

 — Justin

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