Subject: Re: [OAUTH-WG] WGLC review of OAuth 2.0 Security Best Current Practice by Mike Jones

From: Daniel Fett <[email-masked]>
Date: Wed, 22 Jan 2020 15:35:02 +0100

Thanks for your feedback, Mike! I have two questions below:

Am 20.11.19 um 04:40 schrieb Mike Jones:
>
> I did a complete read of draft-ietf-oauth-security-topics-13
> <https://tools.ietf.org/html/draft-ietf-oauth-security-topics-13>.  My
> review comments follow, divided into substantive and editorial sections.
>
>  
>
> SUBSTANTIVE
>
>  
>
> 3.1.2. Implicit Grant – The statement “no viable mechanism exists to
> cryptographically bind access tokens issued in the authorization
> response to a certain client” isn’t actually true.  Please describe
> how the OpenID Connect ID Token achieves this for the “id_token token”
> and “code id_token token” response types via the “at_hash” claim in
> this paragraph, and appropriately qualify the unconditional statement
> cited.

How does the at_hash in the ID token bind the token to the client? I do
see that the client would not accept a token issued for another client.
What is discussed here, however, is that a malicious resource server
could use the token at another resource server. This is not prevented,
or is it?

> 4.8.1.3. Audience Restricted Access Tokens, next to last paragraph –
> When you list MTLS, also please state that the MTLS key can be used as
> a correlation handle, since it is the same for connections to all sites.
>
Wouldn't it be up to the client to use or not use the same key for
multiple sites? Also, what would be the impact of correlation here?