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 <aa...@parecki.com>
Sent: Thursday, May 7, 2020 4:39 PM
To: Dick Hardt <dick.ha...@gmail.com>
Cc: OAuth WG <oauth@ietf.org>; Torsten Lodderstedt <tors...@lodderstedt.net>;
Mike Jones <michael.jo...@microsoft.com>
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
<dick.ha...@gmail.com<mailto:dick.ha...@gmail.com>> 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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