[OAUTH-WG] What's the use case for signing OAuth 2.0 requests?

[Yaron Goland <[e-mail]>]

My understanding of Eran's article (http://hueniverse.com/2010/09/oauth-2-0-without-signatures-is-bad-for-the-web/) is that Eran believes that bearer tokens are not good enough as a security mechanism because they allow for replay attacks in discovery style scenarios. He then, if I understood the article correctly, argues that the solution to the replay attack is to sign OAuth 2.0 requests.
In http://www.goland.org/bearer-tokens-discovery-and-oauth-2-0/ I tried to demonstrate that in fact one can easily prevent replay attacks in discovery scenarios using OAuth 2.0 and bearer tokens. If the article is correct then it is not a requirement to introduce message signing into OAuth 2.0 in order to prevent the attacks that Eran identified.

So this leaves me wondering, what's the critical scenario that can't be met unless we use sign OAuth 2.0 requests?

                Thanks,

                                                Yaron