* Is there an example of an OAuth 2.0 server that can't use bearer tokens for 
protected resource requests and thus requires signatures?

The use case I see for signatures that isn't solved (as well) by tokens is 3 
way integrations where  it is useful to manage a secret as a way to manage the 
business relationship.  I have also seen a lot of cases where the 3rd party 
doesn't want to go SSL  (I'm not gonna try to justify this, it's just how 
things have worked that I've seen).

From: oauth-boun...@ietf.org [mailto:oauth-boun...@ietf.org] On Behalf Of David 
Recordon
Sent: Monday, September 27, 2010 9:58 PM
To: OAuth WG
Subject: [OAUTH-WG] Signatures...what are we trying to solve?

If you know me then you'll know that I'm generally one of the last people to 
talk about Alice and Bob. That said, there are a lot of technical proposals 
flying across the list with very little shared understanding of the problem(s) 
we're trying to solve.

>From what I've seen there are two distinct classes of signature use cases.
1) The first is where the HTTP request parameters must be part of the 
signature. An example is any OAuth 1.0a style API where you want to make sure 
that the HTTP POST your server just received isn't masquerading itself as a GET.
2) The second is where the HTTP request is orthogonal. An example is OpenSocial 
where the server is sending state information to the client such as what user 
is currently logged in.

The main practical example I have of the first use case is what Twitter wants 
to do with redelegation. In this case TweetDeck can't given TwitPic it's own 
bearer token, but needs to sign the POST request and pass that signature to 
TwitPic for it to include in the final API request to Twitter.

In terms of signing protected resource requests, I haven't heard anyone bring 
up specific and detailed needs for this recently.

JSON tokens pretty clearly make sense for the second class of signature use 
cases and it's actually a bit hard to argue why they would be a part of OAuth. 
Facebook shipped this a bit over a month ago for canvas applications. We 
include a `signed_request` parameter which is signature.base64url(JSON). 
Parsing it is 18 lines of PHP. 
http://developers.facebook.com/docs/authentication/canvas

This second class of use case will also be required by OpenID Connect where the 
server is signing identity information and sending it to the client. I imagine 
that OpenSocial will also still have it and wish to continue relying on public 
key algorithms.

So a few questions:
 * Do we want to tackle both of these classes of signatures in OAuth?
 * Why do you consider the second class part of OAuth versus something 
completely separate that might happen to include an OAuth access token?
 * Is the Twitter redelegation use case the right focus for the first class?
 * Is there an example of an OAuth 2.0 server that can't use bearer tokens for 
protected resource requests and thus requires signatures?

Thanks,
--David
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