[Openid-specs-heart] Feedback on the HEART OAuth and OpenID Connect profiles from Mike Jones

Mon May 9 18:51:33 UTC 2016

Mike Jones is onto something that may create difficulties for HEART.  In the cross-industry world, where healthcare is an equal partner with other industries, how much interoperability is required?  OAuth and UMA imply, at least to me, rather broad interoperability where one might have one place to express privacy requirements that apply to many different aspect of one's life.  I suspect that the current US-centric boundaries for what is and isn't health IT are more porous and less worldwide that we might have assumed.

I would like to see some traceability from business and policy requirements to the technical profiles.  For example, is the assumption of having an indeterminate number of AS services with real-time discovery required by business or policy, or is an eventual goal.  How much new infrastructure is needed, and who will bear the costs and responsibility for it?

Glen F. Marshall
Consultant
Security Risk Solutions, Inc.
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From: Openid-specs-heart [mailto:openid-specs-heart-bounces at lists.openid.net] On Behalf Of Justin Richer
Sent: Sunday, May 8, 2016 08:26
To: Mike Jones <Michael.Jones at microsoft.com>; openid-specs-heart at lists.openid.net
Subject: Re: [Openid-specs-heart] Feedback on the HEART OAuth and OpenID Connect profiles from Mike Jones

Hi Mike,

Thanks for the thorough review. It's clear to me that for the most part the specs lack the appropriate justification for the decisions made therein, something that we've started to address with the latest draft changes. I'll go through each point below in turn when I get a chance later this week, but for example: the requirement for introspection at the OAuth AS is to allow interoperable onboarding of RS's. Instead of leaving this as an implementation choice, we are mandating the availability of this connection mechanism for interop. If you've got an embedded RS with your AS, you don't need to use it, but you need to make it available from the AS in order to allow other RS's to connect to you. Note: this is not a requirement of a Connect IdP that's not also acting as an OAuth AS (this point has been clarified in the latest drafts that I linked to the list the other day, I'd ask that you take a look at the new text, please!). Interestingly, you find JWT reasonable and introspection not reasonable, while others have had the opposite view. Therefore we need to clearly state why we have both, as we've attempted to do in the current draft:

http://openid.bitbucket.org/HEART/openid-heart-oauth2.html#rfc.section.4.2

We realize that some of the decisions in the profiles are departures from what's common on OAuth systems, and that's OK. The goal of HEART is not to document what people are already doing, but instead to push the boundary of security and interoperability for this and possibly other vertical domains.

 -- Justin
On 5/8/2016 1:27 AM, Mike Jones wrote:
The 27 review feedback items below are based upon a complete read of the HEART OAuth and OpenID Connect profiles during the Implementer's Draft review follows.  I believe that all the comments equally apply to the current working group drafts.  I've used links to the Implementer's Drafts below since these are stable references to immutable versions.  They are intended to make the profiles clearer, more easily understood, more easily implemented, and more secure.

OAuth Profile - http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.1.1
2.1.1.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.1.1> Full Client with User Delegation<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#FullClient>

(1)  Why is this called a "full client"?  Wouldn't a more descriptive name be something more aligned with OAuth naming, like "Client using Authorization Code Flow" or with OpenID Connect naming, like "Basic Client"?

(2)  Especially in light of the OAuth mix-up attacks, wouldn't it be better for these clients to use, or at least be allowed to use, "response_type=id_token code", rather than be required to use "response_type=code"?

(3)  What is the "unique key" that is RECOMMENDED used for, how is it used, and what restrictions are there on the key type?  For instance, is it assumed to be an asymmetric key?  Are there required or recommended algorithms to use, such as "RS256"?  The spec should say more about this in the interests of both interoperability and clarity.

(4)  What are the implications of not having the "unique key" (not following the RECOMMENDED)?  Why is this RECOMMENDED, rather than REQUIRED?  For one thing, not having this key would seem to conflict with the requirement in 2.2 to use private_key_jwt client authentication.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.1.2
2.1.2.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.1.2> Browser-embedded Client with User Delegation<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#BrowserClient>

(5)  Why is this called "Browser-embedded Client" when this flow could also be used by non-browser applications?  Why not follow the OAuth and Connect naming conventions and call this an "Implicit Client"?

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.1.3
2.1.3.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.1.3> Direct Access Client<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#DirectClient>

(6)  What is the use case behind the decision for the profile to include use of the Client Credentials flow, especially when this bypasses user involvement and user consent?  Is including this actually necessary?  Many servers don't support this, by design.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.2
2.2.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.2.2> Requests to the Token Endpoint<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#RequestsToTokenEndpoint>

(7) The text "MAY use other asymmetric signature methods listed in the JSON Web Algorithms (JWA<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#RFC7518> [RFC7518]) specification" should actually refer to the IANA JSON Web Signature and Encryption Algorithms registry at http://www.iana.org/assignments/jose/jose.xhtml#web-signature-encryption-algorithms - not the JWA spec.

(8)  The paragraph including "Authorization servers MAY require some clients to additionally authenticate using mutual Transport Layer Security (TLS) authentication" is problematic in several ways.  First, how does the server communicate to the client that mutual TLS is required?  How is the client TLS key registered with the server?  Is support for mutual TLS required of servers?  Of clients?  If it's not required, how is interop assured when it is used?

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.3
3.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.3> Client Registration<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#ClientRegistration>

(9)  The profile requires that "each client instance MUST receive a unique client identifier from the authorization server".  This isn't how most OAuth deployments work today - particular for native applications.  Is this significant departure from existing practice truly necessary or is this just a preference?  If it's necessary, the specification should clearly say why.  If it's not truly necessary, this requirement should be downgraded to being a recommendation.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.3.2
3.2.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.3.2> Dynamic Registration<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#DynamicRegistration>

(10)  The profile requires the use of Dynamic Registration.  This is another significant departure from existing practice.  Like the previous comment, this requirement either needs to be justified as being essential or downgraded to being a recommendation.

(11)  The profile indicates that servers MAY accept software statements.  How does the server communicate to clients that it supports software statements or not?  How does it communicate whether their use by clients is required or not?  How does it communicate to developers and clients what kinds of software statements will be accepted and rejected?

(12)  The profile requires that authorization servers "MUST indicate to the end user that such a statement was used in the client's registration".  This seems beyond silly, as most normal people would have no clue what such a message means or how they should respond to it (or the lack of it).  Requiring another "Click OK" barrier in the UI that people won't understand and will just click through won't help either usability or security.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.4
4.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.4> OAuth 2.0 Server Profile<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#ServerProfile>

(13)  The profile requires that "The authorization server MUST limit each registered client (identified by a client ID) to a single grant type only".  This may or may not be fine but doesn't match existing practice for many implementations and the requirement isn't justified in the specification.  At a minimum, clear rationale for this requirement needs to be included.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.4.1
4.1.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.4.1> Discovery<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#Discovery>

(14)  The profile requires support for the introspection endpoint.  This unnecessarily increases the implementation footprint of both clients and servers, increases run-time cost of common operations, and is a significant deviation from most deployments.  If, for instance, the UMA profile requires introspection for some reason, add it there, but do not require HEART OAuth or Connect to support introspection.  This must be removed from the OAuth profile.

(15)  The profile requires support for the revocation endpoint.  This unnecessarily increases the implementation footprint of both clients and servers and is a significant deviation from most deployments.  If, for instance, the UMA profile requires revocation for some reason, add it there, but do not require HEART OAuth or Connect to support revocation.  This must be removed from the OAuth profile.

(16)  The profile states "It is RECOMMENDED that servers provide cache information through HTTP headers and make the cache valid for at least one week."  How does this interact with the need to immediately rotate keys upon key compromise?  Is this saying that a compromised key must remain valid for at least a week?  If this isn't implied by this recommendation, please explain what is actually implied for clients and servers.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.4.2
4.2.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.4.2> JWT Bearer Tokens<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#JWTBearerTokens>

(17)  The spec is unclear what kinds of bearer tokens are being referred to here.  Is it saying that access tokens must be JWTs?  Is it saying that refresh tokens must be JWTs?  This is certainly a reasonable implementation choice but the specification does not clearly state why this is a requirement.  Please say why bearer tokens must be JWTs.

(18)  The profile says that an audience may be included.  Why is the audience not required?  What are the implications of sending and accepting bearer tokens that aren't audience?

(19)  The profile requires including "azp" in JWT bearer tokens.  It's now widely held by the OpenID Connect working group that "azp" is both underspecified and its inclusion in OpenID Connect was a mistake.  (See https://bitbucket.org/openid/connect/issues/973/core-2-3137-azp-claim-underspecified-and - Core 2 / 3.1.3.7 - azp claim underspecified and overreaching.)  Please remove all uses of "azp" from the HEART specifications.  If the client ID needs to be conveyed, an appropriate new well-specified claim should be defined and used for this purpose.

http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.5
5.<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#rfc.section.5> Requests to the Protected Resource<http://openid.net/specs/openid-heart-oauth2-1_0-ID1.html#RequestsToProtectedResource>

(20)  The profile says that resources may support the query-parameter parameter method from RFC 6750.  This is a terrible security mistake.  Change the text to say that "Resources MUST NOT support the query-parameter parameter method from RFC 6750".

OpenID Connect Profile - http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html

http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.2
2.<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.2> ID Tokens<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#IDTokens>

(21)  The profile says that "The ID Token MUST expire and SHOULD have an active lifetime no longer than five minutes".  While this expiration time may be a reasonable implementation choice, the specification is silent on why this reasonably short expiration time is a requirement.  Please either justify this requirement or downgrade this text to a non-normative discussion on criteria for choosing appropriate ID Token lifetimes.

http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.3
3.<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.3> UserInfo Endpoint<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#UserInfoEndpoint>

(22)  The profile requires supporting signed UserInfo responses.  This may be a reasonable thing for the profile to require but the specification fails to motivate this requirement.  Please do so.

(23)  The profile talks about encrypted UserInfo responses but doesn't say whether support for these is required for clients or servers, or why.  Please do so.

http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.4
4.<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.4> Request Objects<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#RequestObjects>

(24)  The profile requires that servers support request objects.  This may be a reasonable thing for the profile to require but the specification fails to motivate this requirement.  Please do so.

http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.5
5.<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#rfc.section.5> Authentication Context<http://openid.net/specs/openid-heart-openid-connect-1_0-ID1.html#AuthenticationContext>

(25)  The profile uses URIs for FICAM LOA numbers as "acr" values.  This seems short-signed and limiting, as these values are specific to the United States and not international in nature.  These must be changed to appropriate international equivalents - especially in coordination with other working groups, such as MODRNA.

(26)  Remove the requirement to support the introspection endpoint from this profile, for the same reasons as in (14).

(27)  Remove the requirement to support the revocation endpoint from this profile, for the same reasons as in (15).

                                                          Thanks all,
                                                          -- Mike]

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