Exactly!
I believe that this also the same point that Brian Campbell was making earlier
about interoperability implications.
-- Mike
From: Neil Madden <[email protected]>
Sent: Sunday, May 10, 2020 1:06 PM
To: Dick Hardt <[email protected]>
Cc: Mike Jones <[email protected]>; [email protected]; Torsten
Lodderstedt <[email protected]>
Subject: Re: [OAUTH-WG] Re: OAuth 2.1 - require PKCE?
But if an AS upgrades to OAuth 2.1 then it MUST reject authorization requests
that don’t include a code_challenge (section 4.1.2.1), so this will only be
possible when all clients support PKCE.
This makes it impossible for a 2.1-compliant AS to also support non-PKCE 2.0
clients (i.e., the vast majority of them).
I think we can have a 2.1 spec that says clients and servers MUST support PKCE
without this hard-fail clause. Otherwise I can’t see how we’d ever ship with
2.1-compliance enabled out-of-the-box.
— Neil
On 10 May 2020, at 20:38, Dick Hardt
<[email protected]<mailto:[email protected]>> wrote:
Hi Mike, I would consider upgrading to OAuth 2.1 to be voluntary, just as the
other extensions. Similarly, OAuth 1.0 deployments upgrading to OAuth 2.0 was
voluntary.
Would you clarify why you think upgrading to OAuth 2.1 would be mandatory?
On Sun, May 10, 2020 at 12:02 PM Mike Jones
<[email protected]<mailto:[email protected]>>
wrote:
I agree with actively maintaining and improving the OAuth 2.0 specs by adding
enhancements that are voluntary to use. I’ve worked on many such improvements,
including Dynamic Client Registration, Authorization Metadata, the Device Flow,
Token Exchange, DPoP, and support PAR and RAR, etc. The issue that’s the
subject is the current discussion is whether to make use of another
enhancement, PKCE, mandatory in cases where it’s actually not needed, rather
than making its use voluntary like the other enhancements, which I certainly
support.
-- Mike
From: Torsten Lodderstedt
<[email protected]<mailto:[email protected]>>
Sent: Sunday, May 10, 2020 3:15 AM
To: Mike Jones <[email protected]<mailto:[email protected]>>
Cc: Daniel Fett <[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>
Subject: [EXTERNAL] Re: [OAUTH-WG] OAuth 2.1 - require PKCE?
Hi Mike,
Mike Jones
<[email protected]<mailto:[email protected]>>
schrieb am Fr. 8. Mai 2020 um 18:55:
OAuth 2.1 was supposed to not introduce breaking changes.
I cannot remember the WG met that decision. Can you please refer to the
respective thread?
Requiring exact redirect URI matching is already a breaking change. Do you
oppose against this as well?
If you want to do that, please do it in TxAuth instead.
Interesting statement. Does it mean you want to conserve OAuth 2.0 and force
any enhancements/improvements to go into TXAuth? This would cause huge
migration efforts for existing deployments wanting to benefit from those
enhancements.
I think existing deployments are better served by actively maintaining and
evolving the 2.x line. For example, PAR and RAR are attempts to improve OAuth
2.x and make it usable for new use cases. That’s better protection of existing
investments than sending them of to TXAuth.
Kind regards,
Torsten.
-- Mike
From: OAuth <[email protected]<mailto:[email protected]>> On Behalf
Of Daniel Fett
Sent: Thursday, May 7, 2020 11:50 PM
To: [email protected]<mailto:[email protected]>
Subject: Re: [OAUTH-WG] OAuth 2.1 - require PKCE?
+1 to all what Aaron said. Thanks for pointing this out!
We need to address this in the security BCP and this will be a normative change
that affects OpenID Connect Core (just as our current recommendation on the
usage of nonce).
We would then have:
- use PKCE, except if you use OIDC with a nonce, then you don't need PKCE,
except if you are a public client, then you still need PKCE.
- use state, except if you use PKCE, then you don't need state.
I think there are very good reasons to simplify this down to
- use PKCE
- you may or may not use state
First and foremost, not many people will understand why there are cases when
the BCP/OAuth 2.1 mandate PKCE and some where they don't. However,
understanding why you have to do something is key to compliance. The short
version "PKCE protects the code; there is a specific case where it is not
needed, but its better to use it all the time" is easy to understand. We will
not see many implementations following the long version above correctly.
Second, we dramatically reduce technical complexity by reducing cases that need
to be handled. We reduce correctness and compliance testing complexity in the
same way. We reduce the cost of security analysis, which scales really badly to
more cases.
And finally, using nonce to protect against code injection is less robust than
PKCE. AS have a better track record than clients when it comes to correctly
implementing security mechanisms.
Yes, this will make a number of implementations non-spec-compliant, but I do
not think that this is a huge problem. Software needs to adapt all the time and
a software that has not been changed in a while is probably not one you would
want to use anyway. We are setting a new goal for implementations to meet and
eventually, maintained implementations will get there.
-Daniel
Am 08.05.20 um 01:38 schrieb Aaron Parecki:
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
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