So you would be doing based on something like the address of the requestor or 
the content of the request.  I would complete understand the first half.  Is 
there any way to prevent a rouge requestor from asking for information – or are 
you just relying on a closed system?

 

From: Cigdem Sengul [mailto:cigdem.sen...@gmail.com] 
Sent: Wednesday, October 25, 2017 2:19 PM
To: Jim Schaad <i...@augustcellars.com>
Cc: Ludwig Seitz <ludwig.se...@ri.se>; ace@ietf.org
Subject: Re: [Ace] Question about the response to an unauthorized request

 

UMA assumes that  resource server knows “which authorization server to approach 
for the permission ticket and on which resource owner's behalf” deriving “the 
necessary information using cues provided by the structure of the API where the 
resource request was made, rather than by an access token. “

On Wednesday, October 25, 2017, Jim Schaad <i...@augustcellars.com 
<mailto:i...@augustcellars.com> > wrote:

How does the RS make an informed decision about who the client is given that it 
is a tokenless access request?

 

 

 

From: Ace [mailto:ace-boun...@ietf.org 
<javascript:_e(%7B%7D,'cvml','ace-boun...@ietf.org');> ] On Behalf Of Cigdem 
Sengul
Sent: Wednesday, October 25, 2017 7:28 AM
To: Ludwig Seitz <ludwig.se...@ri.se 
<javascript:_e(%7B%7D,'cvml','ludwig.se...@ri.se');> >
Cc: ace@ietf.org <javascript:_e(%7B%7D,'cvml','ace@ietf.org');> 
Subject: Re: [Ace] Question about the response to an unauthorized request

 

Hello,

 

To bring a different view, I wanted to mention Kantara UMA (User Managed 
Access) approach to this problem. (I participated in the UMA v2.0 development 
this year, so had the chance to be more familiar with the new drafts.)

 

In UMA,  the resource server must respond to a client's tokenless 
(unauthorized) access attempt by obtaining a permission ticket from the 
authorization server.

If RS is able to obtain a permission ticket from the AS, RS returns this ticket 
to the client also with  the AS uri to aid AS discovery. 

 

UMA handles resources (resource sets, permissions etc.) differently but the 
permission requests (from RS to AS)  can be considered as signaling to the AS 
what audience/scope RS expects.

 

In ACE, there are limitations of course - i.e., RS may not always reach AS etc. 
 Nevertheless, it may be useful to think how other groups approach similar 
problems. 

 

Best, 

--Cigdem 

 

 

On Mon, Oct 23, 2017 at 2:38 PM, Ludwig Seitz <ludwig.se...@ri.se 
<javascript:_e(%7B%7D,'cvml','ludwig.se...@ri.se');> > wrote:

Hello ACE,

Jim Schaad has brought up an interesting question [1] on 
draft-ietf-ace-oauth-authz [2]:

Currently when a client makes an unauthorized request to a resource server, it 
gets back the address of the authorization server and optionally a nonce (to 
prevent replay attacks).

Jim is suggesting to add hints to the audience and scope the resource server 
expects for accessing this resource.

I'm not sure whether that would not reveal too much information to a potential 
attacker.

What does the group think of this issue?

/Ludwig


[1] https://github.com/ace-wg/ace-oauth/issues/124
[2] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-08#section-5.1.2
-- 
Ludwig Seitz, PhD
Security Lab, RISE SICS
Phone +46(0)70-349 92 51 <tel:%2B46%280%2970-349%2092%2051> 

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