Re: [OAUTH-WG] Benjamin Kaduk's No Objection on draft-ietf-oauth-resource-indicators-05: (with COMMENT)

Brian Campbell <bcampbell@pingidentity.com> Wed, 04 September 2019 23:19 UTC

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From: Brian Campbell <bcampbell@pingidentity.com>
Date: Wed, 4 Sep 2019 17:19:27 -0600
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To: Benjamin Kaduk <kaduk@mit.edu>
Cc: The IESG <iesg@ietf.org>, draft-ietf-oauth-resource-indicators@ietf.org, oauth <oauth@ietf.org>, oauth-chairs@ietf.org
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Subject: Re: [OAUTH-WG] Benjamin Kaduk's No Objection on draft-ietf-oauth-resource-indicators-05: (with COMMENT)
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Thanks Ben, for the review and non-objectional ballot.

On Wed, Sep 4, 2019 at 3:13 PM Benjamin Kaduk via Datatracker <
noreply@ietf.org>; wrote:

> Benjamin Kaduk has entered the following ballot position for
> draft-ietf-oauth-resource-indicators-05: No Objection

----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
> Abstract
>
> This seems to be a sentence fragment (maybe preface with "This document
> specifies"?).
>

Hrm. Yeah, I suppose so. I guess I was trying to be efficient with the
words but to the point of not having a complete sentence. I'll add that
preface.



> Section 2.1
>
>    For authorization requests sent as a JWTs, such as when using JWT
>    Secured Authorization Request [I-D.ietf-oauth-jwsreq], a single
>    "resource" parameter value is represented as a JSON string while
>    multiple values are represented as an array of strings.
>
> jwsreq includes an example with "aud" in the request, yet this new
> "resource" request parameter is also intended to influence the audience
> of the resulting token.  I'm not sure whether we need to say anything
> specifically about this in the document, but I'd like to have a better
> understanding of how "aud" and "resource" would interact when both
> present in the reqeust.
> (This is presumably related to why the request parameter is called
> "resource" and not "aud" or "audience", but unfortunately I seem to have
> zoned out for that part of the WG discussion.)
>

In the context of a jwsreq request the "aud" indicates the intended
recipient/audience of the singed authorization request itself, which will
be the authorization server to whom the request is being made. This
prevents a singed request meant for AS1 from being used successfully at
AS2, for example. That "aud" does not do anything to influence the audience
of the resulting token - it's really just metadata of the signed request
that will be discarded once the singed request is validated. The "resource"
parameter of this document indicates where the client intends to use the
token its requesting, which can and will influence the audience of the
resulting token. So "aud" and "resource" do not interact when both present
in a signed authorization request.

And yes, this is related to why the request parameter is called "resource"
and not "aud" and also I think related to the outstanding discuss you have
on jwsreq. If this parameter were to have been called "aud" then there
would be a name collision when used in conjunction with jwsreq where "aud"
would have had two distinct and irreconcilable meanings at the same time.
There are a few other reasons the WG landed on "resource" as the name but
what you've alluded to up here was a big part of it.



   If the client omits the "resource" parameter when requesting
>    authorization, the authorization server MAY process the request with
>    no specific resource or by using a pre-defined default resource
>    value.  [...]
>
> Would/could this default value be global or on a per-scope basis or some
> other finer granularity than global?
>

Yes, it could be any of those. Though I think most likely it'd be global or
influenced by scope. Really, it'd be whatever that AS was doing in the
absence of such a parameter before this document came along.



>                                                                      The
>    authorization server might use this data to inform the user about the
>    resources the client is going to access on her behalf, to meet policy
>    decision (e.g. refuse the request due to unknown resources), and
>    determine the set of resources that can be used in subsequent access
>    token requests.
>
> nits: comma after "e.g.", and maybe s/meet policy decision/apply policy/
> (or similar), and "to" before "determine" for parallelism.
>

Okay, will do.



> In Figure 1 we URL-encode the '.'s in "client.example.org" but not in
> "api.example.com" in the request URL; should we be consistent?  (This
> seems to be recurring throughout the examples.)
>

Shoot. I really do aim to be tighter with that kind of thing well before
getting to the IESG evaluation phase. I suspect some copy/paste/change work
along with not looking closely enough got the better of me here. I'll fix
to use not-encoded '.'s throughout.



> Section 2.2
>
>    needs to know.  This further improves privacy as scope values give an
>    indication of what services the resource owner uses and downscoping a
>    token to only that which is needed for a particular service can limit
>    the extent to which such information is revealed across different
>    services.  As specified in Section 5.1 of [RFC6749], the
>
> (nit?) I suggest to s/scope values give an indication of what services
> the resource owner uses and/a list of scope values is an indication that
> the
> resource owner uses the multiple various services listed;/ since I
> misparsed it the first time as-is.
>

Sure. Striving to avoid the ol' misparse is always good.



> Section 3
>
>    An access token that is audience restricted to a protected resource
>    that obtains that token legitimately cannot be used to access
>    resources on behalf of the resource owner at other protected
>    resources.  The "resource" parameter enables a client to indicate the
>
> nit: This sentence has a pretty strange construction.  I think the
> intent is to say that that a token, legitimately presented to a
> resource, cannot then be taken by that resource server and
> illegitimately present it somewhere else for access to other resources.
> But with the current wording we seem to be missing part of the part
> where some entity obtains the token with intent for illegitimate access.
>

Yes, despite the pretty strange construction, you have the correct intent.
I'll work on improving that sentence (borrowing heavily from your words
there).



>    Some servers may host user content or be multi-tenant.  In order to
>    avoid attacks that might confuse a client into sending an access
>    token to a resource that is user controlled or is owned by a
>    different tenant, it is important to use a specific resource URI
>    including a path component.  This will cause any access token issued
>    for accessing the user controlled resource to have an invalid
>    audience if replayed against the legitimate resource API.
>
> I'm not entirely sure what this is trying to say.  What is the
> "legitimate resource API"?  Why would a token be issued for accessing a
> user-controlled resource if that's something we're trying to avoid
> having confused clients access?
>

Um... so on rereading that I might say that it's also "pretty strange".

What it was trying to somehow say is similar to the previous nit about
audience-restricted not being usable at the resource for whom the weren't
intended. But saying so in the context of a multi-tenant environment.
Basically it's trying to say that, in a multi-tenant environment, the
resource URI and subsequent token audience need to have something that
identifies the tenant so as to prevent the token from being used by one
tenant to illegitimately access resources at a different tenant. I'll work
on trying to improve that text to better explain all that.


   Although multiple occurrences of the "resource" parameter may be
>    included in a request, using only a single "resource" parameter is
>    encouraged.  A bearer token that has multiple intended recipients
>    (audiences) indicating that the token is valid at more than one
>    protected resource can be used by any one of those protected
>    resources to access any of the other protected resources.  Thus, a
>    high degree of trust between the involved parties is needed when
>    using access tokens with multiple audiences.  Furthermore an
>    authorization server may be unwilling or unable to fulfill a token
>    request with multiple resources.
>
> Do we want to contrast this with an authorization code/refresh token,
> which may be more likely to be issued with a multiple-resource/audience
> property?
>

Yeah, it's perhaps worth making the distinction. Though I don't know that
it needs to be explicitly contrasted per se. I think just qualifying the
text above to more specifically say "... parameter may be included in a
token request" (as apposed to authorization request) would be enough to
indicate that the suggestion is only applicable to the access token and not
authorization code/refresh token.

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