I agree that we’re getting dangerously close to recommending signed assertions 
at every step of the process, thereby bypassing HTTP. This was the same mistake 
that WS-* and SOAP made, let’s not repeat it if we can.

 — Justin

> On Apr 30, 2016, at 10:57 AM, Torsten Lodderstedt <[email protected]> 
> wrote:
> 
> Hi Nat,
> 
> sure, one could also authenticate and cryptographically protect the redirect 
> response. Leveraging OIDC concepts is an idea worth considering but they 
> should be adopted to the OAuth philosophy. The id token as used in the hybrid 
> flows mixes an identity assertion with elements of transport security 
> measures. A OAuth AS does not provide identity data to clients, so we only 
> need the transport security part. 
> I personally would prefer a OAuth response object (similar to request object 
> you have proposed) over the id token. Such a response object could contain 
> (and directly protect) state, code and other response values. I consider this 
> the more elegant design and it is easier to implement then having detached 
> signatures over hash values of codes or access tokens. Moreover, it would 
> allow to encrypt the response as well. 
> Generally, our threat analysis so far does not have provided justification 
> for cryptographically protected redirect responses. All proposals currently 
> on the table stop mix up and code injection using simpler mechanisms. 
> I think OAuth 2.0 is a huge success due to its balance of versatility, 
> security and _simplicity_. We definitely need to keep it secure, but we 
> should also keep it as simple as possible.
> kind regards,
> Torsten.
> Am 29.04.2016 um 10:08 schrieb Nat Sakimura:
>> As I look at it more and more, it started to look like the problem of 
>> accepting tainted values without message authentication. To fix the root 
>> cause, we would have to authenticate response. ID Token was designed to also 
>> serve as a solution anticipating it. 
>> 
>> Any concrete ideas? 
>> 
>> On Sat, Apr 23, 2016 at 04:47 Torsten Lodderstedt <[email protected] 
>> <mailto:[email protected]>> wrote:
>> Hi all,
>> 
>> discussion about Mix-Up and CnP seems to have stopped after the session
>> in BA - at least in the OAuth WG. There is a discussion about
>> mitigations in OpenId Connect going on at the OpenId Connect mailing list.
>> 
>> I'm very much interested to find a solution within the OAuth realm as
>> I'm not interested to either implement two solutions (for OpenId Connect
>> and OAuth) or adopt a OpenId-specific solution to OAuth (use id! tokens
>> in the front channel). I therefore would like to see progress and
>> propose to continue the discussion regarding mitigations for both threats.
>> 
>> https://tools.ietf.org/html/draft-ietf-oauth-mix-up-mitigation-00 
>> <https://tools.ietf.org/html/draft-ietf-oauth-mix-up-mitigation-00>
>> proposes reasonable mitigations for both attacks. There are alternatives
>> as well:
>> - mix up:
>> -- AS specific redirect uris
>> -- Meta data/turi
>> (https://tools.ietf.org/html/draft-sakimura-oauth-meta-07#section-5 
>> <https://tools.ietf.org/html/draft-sakimura-oauth-meta-07#section-5>)
>> - CnP:
>> -- use of the nonce parameter (as a distinct mitigation beside state for
>> counter XSRF)
>> 
>> Anyone having an opinion?
>> 
>> best regards,
>> Torsten.
>> 
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