Hi Denis,
Hi Dick and Hannes,
1) While reading RFC 7519, no reader may be able to figure out that there are
more than two flavours of the "sub" claim.
This draft is introducing two new other favours of the semantics of the
"sub" claim which are not present in RFC 7519.
When an element has been defined, its semantics cannot be changed ...
unless making an Errata to RFC 7519
which would be a clean way to proceed.
[Hannes] What do you mean by “flavours” of the subject claim?
2) The argument about "changing the token format at any time" does not apply in
the context of this future RFC.
This sentence should be either removed or modified This means that the
following sentence which is a derivative
of this sentence should also be either removed or modified:
Hence, any logic in the client relying on the ability to read the access token
content would break without recourse.
[Hannes] The OAuth 2.0 architecture allows the authorization server and the
resource server to agree on whatever token format they want. They can pass the
information by value or by reference (which may then require token
introspection or an equivalent mechanism). This document does not change
anything concern this.
Imagine a third party implementing an OAuth 2.0 Client. If they make
assumptions about the ability to parse the content of the token, we create a
brittle system.
For this reason, the sentence "changing the token format at any time" is
correct.
I hope this makes sense.
3) The following questions have still not been answered:
Some questions raised during the WGLC have not been answered: How can a client
request an access token compliant to this profile ?
[Hannes] The client cannot request the authorization server to use a specific
token format. Since the client is not going to look at the access token content
why would it even care.
Which parameter(s) allow it to ask an access token compliant to this profile ?
[Hannes] There no parameters defined so that the client can ask for an access
token format that is compliant to this profile.
How can the AS know that it got a call for the issuance
of an access token compliant to this profile ?
[Hannes] The AS only gets a request for an access token and the AS needs to
decide what format to use, like it did in the past. Nothing changed.
Ciao
Hannes
Denis
Denis
The objective of this document is to standardize the token the AS shares with
the RS. It is not to standardize how the client can read the token. Just
because the user is using the client, that does not mean the user wants the
client to see any claims about themselves. Letting the client see the contents
of the token may be a privacy violation.
client != user
ᐧ
On Tue, Sep 8, 2020 at 9:10 AM Denis
<[email protected]<mailto:[email protected]>> wrote:
Hi Hannes,
Two comments between the lines.
Hi Victorio, Hi all,
I am doing my shepherd write-up for draft-ietf-oauth-access-token-jwt-07.
Reading through the draft I have a few minor suggestions:
Section 2:
I would delete this sentence "JWT access tokens are regular JWTs complying with
the requirements described in this section."
Reason: You pretty much make the same statement on the previous page (see
terminology section).
Section 2.1
s/asymmetric algorithms/asymmetric cryptography
(same replacement in Section 4)
s/ This specification registers the "application/at+jwt" media type,
which can be used to indicate that the content is an access token./This
specification registers the "application/at+jwt" media type,
which can be used to indicate that the content is a JWT access token.
Use capitalized "Section" when a section number is indicated, such as in
Section 2.2.
Section 2.2
s/""aud"/"aud"
2.2.1
s/ auth_time OPTIONAL - as defined in section 2 of [OpenID.Core]./
auth_time OPTIONAL - as defined in Section 2 of [OpenID.Core].
s/ acr, amr OPTIONAL - as defined in section 2 of [OpenID.Core]./ acr, amr
OPTIONAL - as defined in Section 2 of [OpenID.Core].
s/Please see/See
s/For example:/For example,
Section 4
You write:
"Authorization servers SHOULD implement OAuth 2.0 Authorization Server Metadata
[RFC8414] ... "
Are you sure you mean "implement" and not "use"? The paragraph gives me the
impression that you talk about "ASs using RFC 8414"
s/Please see section Section 5 for further guidance on security
implications./Please see Section 5 for further guidance on security
implications.
This sentence sounds strange to me:
"
When invoked as described in OAuth 2.0 Bearer Token Usage [RFC6750],
resource servers receiving a JWT access token MUST validate it in the
following manner.
"
How about:
"
Resource servers receiving a JWT access token MUST validate it in the
following manner.
"
Question: If you refer to RFC 6750 and then list the steps are you just
repeating the steps from RFC 6750 or are you augmenting them?
You write:
"
If the JWT access token includes authorization claims as described in
the authorization claims section, the resource server SHOULD use them
in combination with any other contextual information available to
determine whether the current call should be authorized or rejected.
"
Include a reference to the authorization claims section
s/ For more
details on cross-JWT confusion please refer to 2.8 of [RFC8725]./ For more
details on cross-JWT confusion please refer to Section 2.8 of [RFC8725].
You write:
"
Authorization servers should not rely on the use of different keys
for signing OpenID Connect ID Tokens and JWT tokens as a method to
safeguard against the consequences of leaking specific keys.
"
The phrase "leaking keys" is probably not the best term to describe what
follows afterwards in the text.
You write:
"
The client MUST NOT inspect the content of
the access token
"
This RFC 2119 language is not really enforceable in terms of interoperability.
Maybe you could rephrase a bit. Something like the following would work:
"
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. The OAuth 2.0 framework assumes that access tokens
are treated opaque by clients.
Administrators of authorization servers should also take into account that
the content of an access token is visible to the client. 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.
"
In the general case, the OAuth 2.0 framework assumes that access tokens are
treated as opaque by clients.
However, with this coming RFC, we are not in the general case: since the client
gets back an access token conformant to this RFC, then it knows
exactly its detailed structure. The argument about "changing the token format
at any time" does not apply. In this case, the client is quite sure
that it would be able to understand most of its content (at least all the
standard claims). The above text proposal would need to be reconsidered.
Hiding (by encrypting it) the content of the access token to the client is odd
when an access token contains claims about a human-user :
these claims are personal data and the human-user is usually allowed to have
access to his own personal data.
Encryption is nice in theory but complicated in practice, since a key
management system must put in place. Whenever possible, it should be avoided.
BTW, some questions raised during the WGLC have not been answered: How can a
client request an access token compliant to this profile ?
Which parameter(s) allow it to ask an access token compliant to this profile ?
How can the AS know that it got a call for the issuance of an access token
compliant to this profile ?
Another comment follows.
You wrote:
"
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 confidentiality. 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.
"
The first sentence is a repetition of the previous paragraph. I would suggest
to delete
the first sentence in this paragraph and to move the second sentence to the
previous paragraph.
You wrote:
"
This profile mandates the presence of the "sub" claim in every JWT
access token, making it possible for resource servers to rely on that
information for performing tasks such as correlating incoming
requests with data stored locally for the authenticated principal.
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. 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 tht cannot be
correlated in the event of resource servers collusion. 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. In turn, the client should obtain a new JWT access
token for every call to the resource server, to ensure that the
resource server receives different "sub" and "jti" values at every
call, thus preventing correlation between distinct requests.
"
The above paragraph suggests that there are different levels of privacy. What
you are
talking about in the text is unlinkability and identification. Ways to deal
with such
privacy threats are described in Section 6 of RFC 6973.
Hence, I would suggest to slightly rephrase the paragraph to something like:
"
This profile mandates the presence of the "sub" claim in every JWT
access token, making it possible for resource servers to rely on that
information for correlating incoming
requests with data stored locally for the authenticated principal.
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. The "sub" claim should be
populated by the authorization servers according to a privacy impact
assessment. 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.
While the idea is really nice, the use of the "sub" claim in this context is
not compatible with the definition of the "sub" claim
as defined in RFC 7519:
4.1.2. "sub" (Subject) Claim
The "sub" (subject) claim identifies the principal that is the
subject of the JWT. The claims in a JWT are normally statements
about the subject. The subject value MUST either be scoped to be
locally unique in the context of the issuer or be globally unique.
The processing of this claim is generally application specific. The
"sub" value is a case-sensitive string containing a StringOrURI
value. Use of this claim is OPTIONAL.
There are two options and two options only:
"locally unique in the context of the issuer" means that it is the same for all
RSs.
"globally unique" means that it is the same not only for all the RSs but also
for servers that have nothing to do with OAuth (e.g. an email address).
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. In turn, the client should obtain a new JWT access
token for every call to the resource server, to ensure that the
resource server receives different "sub" and "jti" values at every
call, thus preventing correlation between distinct requests.
The proposed text describes two different cases where the sub claim is either
unique for an AS/RS pair or unique for each access token.
These two cases are not included in the definition found in RFC 7519.
In the general case, an identifier can be:
1. locally unique in the context of the issuer (i.e. the same for all RSs),
2. globally unique (i.e. the same not only for all the RSs but also for
servers that have nothing to do with OAuth),
3. unique for an AS/RS pair, or
4. unique for each access token.
I see different ways to solve this problem:
1° Stick to the definition of RFC 7519 and (unfortunately) remove these
possibilities.
2° Define two new claims which would support the two cases where the sub claim
would be either unique for an AS/RS pair or unique for one access token.
3° Define four new claims which would support the four above cases.
Denis
"
Section 7.2
s/ Section Section 2.2.3.1 of this specification refers to the
attributes "roles", "groups", "entitlements" defined in [RFC7643] to
express authorization information in JWT access tokens.
/ Section 2.2.3.1 of this specification refers to the
attributes "roles", "groups", "entitlements" defined in [RFC7643] to
express authorization information in JWT access tokens.
References
RFC 7519 has to be a normative reference:
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519><https://www.rfc-editor.org/info/rfc7519>.
RFC 7644 is an unused reference:
[RFC7644] Hunt, P., Ed., Grizzle, K., Ansari, M., Wahlstroem, E.,
and C. Mortimore, "System for Cross-domain Identity
Management: Protocol", RFC 7644, DOI 10.17487/RFC7644,
September 2015,
<https://www.rfc-editor.org/info/rfc7644><https://www.rfc-editor.org/info/rfc7644>.
The same is true for RFC 3986:
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986><https://www.rfc-editor.org/info/rfc3986>.
Ciao
Hannes
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