Hi Hannes,
Thank you for responses. See below.
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?
[Denis] RFC 7519 states: The subject value MUST *either *be scoped to be
locally unique in the context of the issuer *or *be globally unique.
This makes two flavours: *either *locally unique in the context of the
issuer *or *globally unique.
When reading the current text, in addition to these two flavours, two
additional flavours (3) and (4) are discovered
which makes a total of four flavours:
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, and
4. unique for every access token.
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.
[Denis] I do not dispute the sentence you proposed "The OAuth 2.0
framework assumes that access tokens are treated opaque by clients"
which replaces the previous sentence which was: "The client MUST NOT
inspect the content of the access token".
The two sentences prior to it are:
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.
Once having read your last three responses, I would propose the
following small change in the second sentence:/
/
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 /at an instant of time might /break /later on/
without recourse.
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.
[Denis] While reading all of your three last responses, I now understand
the point.
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.
OK.
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.
Your response does help to understand. Section 3 is stating:
An authorization server /can /issue a JWT access token in response
to any authorization grant defined by [RFC6749] and
subsequent extensions meant to result in an access token.
I believe, it would be worthwhile to add a sentence, just after this
sentence, with the following text:
When an authorization server decides to issue a JWT access token
compliant to this profile, then the following requirements apply.
(...)
Denis
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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