Actually, the first paragraph of the Security BCP section at
https://tools.ietf.org/html/draft-ietf-oauth-security-topics-15#section-2.1.1,
which has gone through WGLC, includes the use of “nonce” to prevent
authorization code injection as a best practice. That’s already a pretty
strong stamp of approval by the OAuth working group.
-- Mike
From: Phillip Hunt <[email protected]>
Sent: Friday, May 8, 2020 12:45 PM
To: Dick Hardt <[email protected]>
Cc: Philippe De Ryck <[email protected]>; Mike Jones
<[email protected]>; OAuth WG <[email protected]>
Subject: Re: [OAUTH-WG] OAuth 2.1 - require PKCE?
We are not discussing anything new here. We are discussing adoption of best
practice.
The disconnect appears to be that one dependent standard’s “typical” use
(nonces) does not have the ietf consensus as best practice.
This lack of consensus needs to be resolved.
Phil
On May 8, 2020, at 12:37 PM, Dick Hardt
<[email protected]<mailto:[email protected]>> wrote:
FYI: An objective of OAuth 2.1 is not to introduce anything new -- it is OAuth
2.0 with best practices.
On Thu, May 7, 2020 at 10:36 PM Philippe De Ryck
<[email protected]<mailto:[email protected]>>
wrote:
From working with a lot of developers on understanding OAuth 2.0 and OIDC, I
definitely vote for simplicity. Understanding the subtle nuances of when a
nonce is fine and when PKCE should be used is impossible without in-depth
knowledge of the flows and their properties. Misunderstandings will cause
security vulnerabilities, which can easily be avoided.
Since OAuth 2.1 is a separate spec, I don’t really see a problem with existing
code not being compliant. They support OAuth 2.0, and if they want to be OAuth
2.1 compliant, they add PKCE. If I’m not mistaken, other requirements of OAuth
2.1 would also clash with existing deployments (e.g., using non-exact redirect
URIs).
I believe that optimizing for making OAuth 2.1 easier to understand will yield
the highest return.
Philippe
On 8 May 2020, at 03:42, Mike Jones
<[email protected]<mailto:[email protected]>>
wrote:
Aaron, I believe you’re trying to optimize the wrong thing. You’re concerned
about “the amount of explanation this will take”. That’s optimizing for spec
simplicity – a goal that I do understand. However, by writing these few
sentences or paragraphs, we’ll make it clear to developers that hundreds or
thousands of deployed OpenID Connect RPs won’t have to change their
deployments. That’s optimizing for interoperability and minimizing the burden
on developers, which are far more important.
As Brian Campbell wrote, “They are not equivalent and have very different
ramifications on interoperability”.
Even if you’re optimizing for writing, taking a minimally invasive protocol
change approach will optimize that, overall. If we proceed as you’re
suggesting, a huge amount of writing will occur on StackOverflow, Medium,
SlashDot, blogs, and other developer forums, where confused developers will ask
“Why do I have to change my deployed code?” with the answers being “Despite
what the 2.1 spec says, there’s no need to change your deployed code.”
I’d gladly write a few sentences in our new specs now to prevent ongoing
confusion and interop problems that would otherwise result. Let me know when
you’re ready to incorporate them into the spec text.
-- Mike
From: Aaron Parecki <[email protected]<mailto:[email protected]>>
Sent: Thursday, May 7, 2020 4:39 PM
To: Dick Hardt <[email protected]<mailto:[email protected]>>
Cc: OAuth WG <[email protected]<mailto:[email protected]>>; Torsten Lodderstedt
<[email protected]<mailto:[email protected]>>; Mike Jones
<[email protected]<mailto:[email protected]>>
Subject: Re: OAuth 2.1 - require PKCE?
Backing up a step or two, there's another point here that I think has been
missed in these discussions.
PKCE solves two problems: stolen authorization codes for public clients, and
authorization code injection for all clients. We've only been talking about
authorization code injection on the list so far. The quoted section of the
security BCP (4.5.3) which says clients can do PKCE or use the nonce, is only
talking about preventing authorization code injection.
The nonce parameter solves authorization code injection if the client requests
an ID token. Public clients using the nonce parameter are still susceptible to
stolen authorization codes so they still need to do PKCE as well.
The only case where OpenID Connect clients don't benefit from PKCE is if they
are also confidential clients. Public client OIDC clients still need to do PKCE
even if they check the nonce.
OpenID Connect servers working with confidential clients still benefit from
PKCE because they can then enforce the authorization code injection protection
server-side rather than cross their fingers that clients implemented the nonce
check properly.
I really don't think it's worth the amount of explanation this will take in the
future to write an exception into OAuth 2.1 or the Security BCP for only some
types of OpenID Connect clients when all clients would benefit from PKCE anyway.
Aaron
On Wed, May 6, 2020 at 10:48 AM Dick Hardt
<[email protected]<mailto:[email protected]>> wrote:
Hello!
We would like to have PKCE be a MUST in OAuth 2.1 code flows. This is best
practice for OAuth 2.0. It is not common in OpenID Connect servers as the nonce
solves some of the issues that PKCE protects against. We think that most OpenID
Connect implementations also support OAuth 2.0, and hence have support for PKCE
if following best practices.
The advantages or requiring PKCE are:
- a simpler programming model across all OAuth applications and profiles as
they all use PKCE
- reduced attack surface when using S256 as a fingerprint of the verifier is
sent through the browser instead of the clear text value
- enforcement by AS not client - makes it easier to handle for client
developers and AS can ensure the check is conducted
What are disadvantages besides the potential impact to OpenID Connect
deployments? How significant is that impact?
Dick, Aaron, and Torsten
ᐧ
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