Re: [OAUTH-WG] Authorization code reuse and OAuth 2.1

I agree that PKCE (with a non-plain operational mode) protects the code from attacker use by the security BCP model (but not necessarily stronger models)

Would the prevalence for ASs which cannot enforce an atomic code grant warrant further language against plain PKCE?

-DW

> On Oct 13, 2021, at 11:16 AM, Mike Jones <Michael.Jones=40microsoft.com@dmarc.ietf.org> wrote:
> 
> During today’s call, it was asked whether we should drop the OAuth 2.0 language that:
>          The client MUST NOT use the authorization code
>          more than once.  If an authorization code is used more than
>          once, the authorization server MUST deny the request and SHOULD
>          revoke (when possible) all tokens previously issued based on
>          that authorization code.”
>  
> The rationale given was that enforcing one-time use is impractical in distributed authorization server deployments.
>  
> Thinking about this some more, at most, we should relax this to:
>          The client MUST NOT use the authorization code
>          more than once.  If an authorization code is used more than
>          once, the authorization server SHOULD deny the request and SHOULD
>          revoke (when possible) all tokens previously issued based on
>          that authorization code.”
>  
> In short, it should remain illegal for the client to try to reuse the authorization code.  We can relax the MUST to SHOULD in the server requirements in recognition of the difficulty of enforcing the MUST.
>  
> Code reuse is part of some attack scenarios.  We must not sanction it.
>  
>                                                           -- Mike
>  
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