Let me try to jump in here in order to make a proposal for the text in
the privacy consideration section:
FROM:
*6*<https://tools.ietf.org/html/draft-ietf-oauth-access-token-jwt-04#section-6>*.
Privacy Considerations*
As JWT access tokens carry information by value, it now becomes
possible for requestors and receivers to directly peek inside the
token claims collection. The client MUST NOT inspect the content of
the access token: the authorization server and the resource server
might decide to change token format at any time (for example by
switching from this profile to opaque tokens) hence any logic in the
client relying on the ability to read the access token content would
break without recourse. Nonetheless, authorization servers should
not assume that clients will comply with the above. Whenever client
access to the access token content presents privacy issues for a
given scenario, the authorization server should take explicit steps
to prevent it as described below.
In scenarios in which JWT access tokens are accessible to the end
user, it should be evaluated whether the information can be accessed
without privacy violations (for example, if an end user would simply
access his or her own personal information) or if steps must be taken
to enforce cofidentiality. Possible measures include: encrypting the
access token, encrypting the sensitive claims, omitting the sensitive
claims or not using this profile, falling back on opaque access
tokens.
In every scenario, the content of the JWT access token will
eventually be accessible to the resource server. It's important to
evaluate whether the resource server gained the proper entitlement to
have access to any content received in form of claims, for example
through user consent in some form, policies and agreements with the
organization running the authorization servers, and so on.
TO:
*6
<https://tools.ietf.org/html/draft-ietf-oauth-access-token-jwt-04#section-6>.
Privacy Considerations*
The design of OAuth 2.0 envisions that access tokens are created by
authorization servers and consumed by resource servers.
As JWT access tokens, as described in this document, carry
information by value, it is
possible for OAuth clients to peek inside the access token.
While this is technical possible, it is important to note that the
OAuth 2.0 protocol does not aim to expose the content of the
access token to the client. The access token is therefore, by
design, considered to be
opaque to the client.
A number of cases may make it difficult or impossible for clients to
inspect the token, for example, the access token may be encrypted,
the access token may contain vendor-specific claims that have not been
standardized or have been standardized in other consortia making
parsing
of the token difficult. Additionally, there is no guarantee that the
access token is conveyed by value and the authorization server
implementation
may change the token format at any time.
In scenarios where it is desirable for the clients to obtain
information
transmitted in the access token, OAuth 2.0 token introspection may
provide
a useful tool to enable such functionality (proper authorization
assumed).
In scenarios where the content of the access token must not be
readable
by clients, encrypting the content of the access token is RECOMMENDED.
Since the content of the access token is accessible to the resource
server
it is important to
evaluate whether the resource server gained the proper entitlement to
have access to any content received in form of claims, for example
through user consent in some form, policies and agreements with the
organization running the authorization servers, and so on. The
policies
and the user interfaces to enable this user consent are, however, part
of a specific deployment and therefore outside the scope of this
document.
How does this sound?
Ciao
Hannes
*From:* OAuth <oauth-boun...@ietf.org> *On Behalf Of * Rifaat Shekh-Yusef
*Sent:* Thursday, May 14, 2020 8:03 PM
*To:* Denis <denis.i...@free.fr>
*Cc:* Vittorio Bertocci <vittorio.berto...@auth0.com>; oauth@ietf.org
*Subject:* Re: [OAUTH-WG] Second WGLC on "JSON Web Token (JWT) Profile
for OAuth 2.0 Access Tokens"
Denis,
You are rehashing the same issues that you have already discussed on
the mailing list multiple times,
You could not get the WG to agree with your points, because the WG
believe that this issue is outside the scope of this document.
The best the chairs can do at this stage is to capture your point in
the shepherd write-up to the IESG.
We think this document has the support of the WG and is ready to
move forward.
Regards,
Rifaat
On Thu, May 14, 2020 at 12:29 PM Denis <denis.i...@free.fr
<mailto:denis.i...@free.fr>> wrote:
Hi Vittorio,
I am referring to the email you sent on April the 29 th which is
copied below.
1) You wrote:
/> targeting of access tokens/
Let me think about that a bit longer.
I acknowledge that the decision of including an audience has
the effect of letting the AS track when the client accesses a
particular resource,
but at the same time that’s completely mainstream and very
much by design in a very large number of cases. As such, I
find the language
you are suggesting to be potentially confusing, as it
positions this as an exception vs a privacy protecting
mainstream that is in fact not common,
and ascribes to the client more latitude than I believe is
legitimate to expect or grant.
*I’ll try to come up with concise language that clarifies to
the reader that the current mechanism does allow AS tracking*.
Since the last draft has been published on the 27 th, you have not
proposed any "concise language that clarifies to the reader
that the current mechanism does allow AS tracking".
2) You also wrote about the "sub" uniqueness:
As long as an identifier identifies one resource only, it
satisfies uniqueness. It doesn’t have to be a singleton.
RFC 7519 defines in section 4.1.2 the semantics of the "sub" claim
using the following sentence:
The subject value MUST either be scoped to be locally unique
in the context of the issuer or be globally unique.
The text does NOT say that the subject value "MUST be scoped to be
locally unique in the context of the *resource server*".
Changing the semantics of an already defined claim is not
permitted. If you would like to have such a semantics available,
a new claim should be defined (and it would be very nice to have
it !).
3) The text is the privacy considerations section states:
Although the ability to correlate requests might be required by
design in many scenarios, there are scenarios where the authorization
server might want to prevent correlation to preserve the
desired level of privacy.
In the real world, it is also clients or end-users which would
like to prevent correlation to preserve their desired level of
privacy.
A better sentence would be:
Although the ability to correlate requests might be required by
design in many scenarios, there are scenarios where the authorization
server *or the client* might want to prevent correlation to
preserve the desired level of privacy.
4) The text continues with:
Authorization servers should choose how to assign "sub" values
according to the level of privacy required by each
situation. For instance: if a solution requires preventing
tracking principal activities across multiple resource servers,
the authorization server should ensure that JWT access tokens
meant for different resource servers have distinct "sub"
values that cannot be correlated in the event of resource
servers collusion.
Authorization servers are not necessarily able to choose the level
of privacy required by each situation. When there are different
situations for the same resource server, the scope is
(unfortunately at the moment) the only way to select the "level of
privacy that is required".
The example ("For instance:") is only an example that provides a
vague recommendation for the ASs which is NOT conformant
with the semantics of the "sub" claim as defined in RFC 7519.
What should be discussed here are not "examples" or what an
authorization server should do, but explanations about the
implications
for the end-user or for the client for the various values that can
be placed into the "sub" claim by an AS. The problem is wider that
simply
a collusion between resource servers, but also with other servers
that DO NOT participate in any OAuth exchange.
RFC 6973 (Privacy Considerations) states in section 7 : Guidelines
This section provides guidance for document authors in the
form of a questionnaire about a protocol being designed.
The questionnaire may be useful at any point in the design
process, particularly after document authors have developed
a high-level protocol model as described in [RFC4101].
One of the questions is:
f. *Correlation*. Does the protocol allow for correlation of
identifiers ? Are there expected ways that information exposed
by the protocol will be combined or *correlated with
information obtained outside the protocol* ?
It is important to provide an answer to these two questions.
Hereafter is some text that is fully conformant with RFC 7519
which should be incorporated into the privacy considerations section
which explains the implications of the two (and only two) flavours
of the "sub" claim.
When the sub claim contains a locally unique identifier in the
context of the issuer, this allows the tracking of principal
activities
across multiple resource servers.
When the sub claim contains a globally unique identifier, this
allows to correlate principal activities across multiple resource
servers, while in addition, this globally unique identifier
may also allow to correlate the principal activities on
servers where
no access has been performed by the principals to these
servers but where the same globally unique identifiers are
being used
by these servers.
Denis
Thanks Denis for the thorough commentary.
/> The title of this spec./
Fixed, thanks!
/> The client MUST NOT inspect the content of the access token/
This is really a sticky point. I really want to acknowledge
your PoV on this, but at the same time I found this to be one
of the biggest sources of issues in the use of JWT for access
tokens hence I feel we really need to give solid guidance
here. Let me expand further on the reasoning behind it, and
perhaps we can get to language that satisfies both PoVs.
To me the key point is that clients should not write /code/
that inspects access tokens. Taking a dependency on the
ability to do so is ignoring fundamental information about the
architecture and relationships between OAuth roles, and
suggests an ability of the client to understand the semantic
of the content that cannot be assumed in the general case. I
expanded on the details in my former reply to you on this
topic, I would recommend referring to it. Clients violating
this simple principle has been one of the most common sources
of production issues I had to deal with in the past few years,
and one of the hardest to remediate given that clients are
hard to update and sometimes the things they relied on were
irremediably lost. This is why I am inclined to put in here
strong language.
That said: I have nothing against client developers examining
a network trace and drawing conclusions based on the content
of what they see. That doesn’t create any hard dependencies
and has no implications in respect to changes in the solution
behavior. However I am not sure how to phrase that in the
specification, given that referring to the client inevitably
refers to its code. I am open to suggestions.
> 3)…
I have a pretty hard time following the chain of reasoning in
this section. Let me attempt to tackle it to the best of my
understanding.
I think the key might be
/> a client should be able to choose whether it wishes the sub
claim to contain [..]/
I don’t think that should be a choice left to the client. In
business systems, my experience is that the type of
identifiers to be used (when the IdP gives any choice at all)
is established at resource provisioning time. I am not aware
of mechanisms thru which a client signals the nature of the
identifier to be used, nor that would be fully feasible (the
resource knows what it needs to perform its function).
Furthermore:
/> which has nothing to do with uniqueness since the value
changes for every generated token./
Again, this is something that was touched on in my former
reply to your message. As long as an identifier identifies one
resource only, it satisfies uniqueness. It doesn’t have to be
a singleton.
Finally, the scope is optional (for good reasons: 1^st party
and non delegation scenarios don’t require it) hence it cannot
be relied upon for properties that should hold in every scenario.
In summary: per the preceding thread on this topic, the
consensus was that varying the sub content was a satisfactory
way of protecting against correlation. I don’t a gree that
clients should have a mechanism to request different sub
flavors, as that decision should be done out of band by the AS
and RS; and the scope isn’t always available anyway.
/> targeting of access tokens/
Let me think about that a bit longer.
I acknowledge that the decision of including an audience has
the effect of letting the AS track when the client accesses a
particular resource, but at the same time that’s completely
mainstream and very much by design in a very large number of
cases. As such, I find the language you are suggesting to be
potentially confusing, as it positions this as an exception vs
a privacy protecting mainstream that is in fact not common,
and ascribes to the client more latitude than I believe is
legitimate to expect or grant.
I’ll try to come up with concise language that clarifies to
the reader that the current mechanism does allow AS tracking.
*From: *OAuth <oauth-boun...@ietf.org>
<mailto:oauth-boun...@ietf.org> on behalf of Denis
<denis.i...@free.fr> <mailto:denis.i...@free.fr>
*Date: *Wednesday, April 29, 2020 at 09:12
*To: *"oauth@ietf.org" <mailto:oauth@ietf.org>
<oauth@ietf.org> <mailto:oauth@ietf.org>
*Subject: *Re: [OAUTH-WG] Second WGLC on "JSON Web Token (JWT)
Profile for OAuth 2.0 Access Tokens"
You will find four comments numbered 1) to 4).
*1) *The title of this spec. is:
JSON Web Token (JWT) Profile for OAuth *2.0* Access Tokens
So, this spec. is supposed to be targeted to OAuth *2.0.
* However, the header at the top of the page omits to mention it.
Currently, it is :
Internet-Draft OAuth Access Token JWT Profile April 2020
It should rather be:
Internet-Draft OAuth *2.0* Access Token JWT Profile April 2020
*2)* The following text is within section 6.
The client MUST NOT inspect the content of
the access token: the authorization server and the resource server
might decide to change token format at any time (for example by
switching from this profile to opaque tokens) hence any logic
in the
client relying on the ability to read the access token content
would
break without recourse.
Nonetheless, authorization servers should
not assume that clients will comply with the above.
It is of a primary importance that clients MAY be able to
inspect tokens before transmitting them.
The "MUST NOT" is not acceptable.
The above text should be replaced with:
Reading the access token content may be useful for the user to
verify that
the access token content matches with its expectations. However,
the authorization server and the resource server might decide
to change the
token format at any time. Thus, the client should not expect
to always be
in a position to read the access token content.
The remaining of the text about this topic is fine.
*3) *The next topic is about the sub claim.
The text states:
Although the ability to correlate requests might be required by
design in many scenarios, there are scenarios where the
authorization
server might want to prevent correlation to preserve the desired
level of privacy. Authorization servers should choose how to
assign
sub values according to the level of privacy required by each
situation.
I have a set of questions:
1. How can authorization servers choose how to assign sub
values according to the level of privacy required "by each
situation" ?
2. How can authorization servers know the level of privacy
required "by each situation" ?
3. How can the users be informed of the level of privacy
required "by each situation" ?
4. How can the users *consent* with the level of privacy
required "by each situation" ?
Currently, the request MUST include either a resource
parameter or an aud claim parameter, while it MAY include a
scope parameter.
The syntax of the scope parameter is a list of
space-delimited, case-sensitive strings (RFC 6749). It is thus
subject to private agreements
between clients and Authorization Servers. Since the scope is
being returned, it is a primary importance that the returned
scope matches
with its expectations before transmitting the token to a
Resource Server.
In theory, a client should be able to choose whether it wishes
the sub claim to contain :
* a global unique identifier for all ASs ("globally unique"),
* a unique identifier for each AS ("locally unique in the
context of the issuer"),
* a different pseudonym for each RS, or
* a different pseudonym for each authorization token request.
The only variable parameter that it can use for this purpose
in the token request is the scope parameter.
RFC 7519 states is section 4.1.2:
The subject value MUST either be scoped to be locally unique
in the context of the issuer
or be globally unique.
It is quite hard to recognize that the sub claim is able to
carry a different pseudonym for each RS, i.e. for case (c), or
a different pseudonym for each authorization token request,
i.e. for case (d), which has nothing to do with uniqueness
since the value changes for every generated token.
This has implications about the following text:
For instance: if a solution requires preventing tracking
principal activities across multiple resource servers, the
authorization server should ensure that JWT access tokens
meant for
different resource servers have distinct sub values that cannot be
correlated in the event of resource servers collusion.
Since it addresses case (c).
and also about the following text:
4.b) Similarly: if a solution requires preventing a resource
server from
correlating the principal’s activity within the resource
itself, the
authorization server should assign different sub values for
every JWT
access token issued.
Since it addresses case (d).
This means that the current text placed in the privacy
considerations section was a good attempt to address the case,
but that the text needs to be revised.
Proposed text replacement for all the previously quoted sentences:
According to RFC 7519 (4.1.2): The subject value MUST either
be scoped to be locally unique in the context of the issuer or
be globally unique.
When the sub claim contains a globally unique identifier, this
allows to correlate principal activities across multiple
resource servers, while in addition,
this globally unique identifier may also allow to correlate
the principal activities on servers where no access has been
performed by the principals
to these servers but where the same globally unique
identifiers are being used by these servers.
When the sub claim contains a locally unique identifier in the
context of the issuer, this also allows the tracking of
principal activities across multiple resource servers.
The scope request parameter is the only way to influence on
the content of the sub claim parameter. Its meaning is subject
to a private agreement
between the client and the AS, which means that the use of the
scope parameter is the only way to choose between a locally
unique identifier
in the context of the issuer or a globally unique identifier.
Since the scope parameter is being returned, it is a primary
importance that the returned scope matches with the
expectations of the client before transmitting
the token to a Resource Server.
However, there are other cases where the client would like to
be able to choose whether it wishes the sub claim to contain :
- a different pseudonym for each RS so that different
resource servers will be unable to correlate its activities, or
- a different pseudonym for each authorization token
request, so that the same resource server cannot correlate its
activities performed at different instant of time.
Considering the semantics of the sub claim, these two cases
cannot be currently supported.
*4) *The next topic is about the targeting of access tokens
Text had been proposed before the last conference call. Then,
the topic has been presented at the very end of the last
conference call, but no text has been included
in the next draft.
Here is a revised text be included in the privacy
considerations section:
For security reasons, some clients may be willing to target
their access tokens but, for privacy reasons, may be unwilling
to disclose to Authorization Servers
an identification of the Resource Servers they are going to
access, so that Authorization Servers will be unable to know
which resources servers are being accessed.
The disclosure of the Resource Servers names allows the
Authorization Servers to list all the Resource Servers being
access by all its users and in addition to list pairs
of (Principal, Resource Servers) which allow to trace all the
users accesses to Resource Servers performed through a given
Authorization Server. When a token is targeted,
this profile does not contain provisions to address these two
threats.
Denis
Hi all,
This is a second working group last call for "JSON Web
Token (JWT) Profile for OAuth 2.0 Access Tokens".
Here is the document:
https://tools.ietf.org/html/draft-ietf-oauth-access-token-jwt-06
Please send your comments to the OAuth mailing list by
April 29, 2020.
Regards,
Rifaat & Hannes
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