Re: [Ace] [OAUTH-WG] Shepherd write-up for draft-ietf-oauth-resource-indicators-01

[Ludwig Seitz <[e-mail]>]

On 28/01/2019 23:12, George Fletcher wrote:
> I also don't know that this raises to the level of "concern" but I find 
> the parameter name of "req_aud" odd. Given that the parameter in the 
> resource-indicators spec is 'resource' why not use a parameter name of 
> 'audience'. That said, I have not read the thread on the ACE working 
> group list so there could be very good reasons for the chosen name:)
> 
> I do think that there is a lot of overlap (in most cases) between 
> 'resource' and 'audience' and having two parameters that cover a lot of 
> the same semantics is going to be confusing for developers. When calling 
> an API at a resource server, the 'audience' and the 'resource' are 
> pretty equivalent. Maybe in other use cases they are distinctly separate?
> 

To give you all the background of "req_aud" from ACE (sorry for the long 
text):

Originally in ACE we had defined the "aud" parameter for requests to the 
token endpoint with the semantics that the client was requesting a token 
for a certain audience (i.e. requesting that the AS copy the "aud" 
parameter value into the "aud" claim value of the token).
We were then told that this collided with a use of "aud" in OAuth, that 
specifies the intended audience of Authorization Servers (if I remember 
correctly), so we decided to rename our parameter to "req_aud" for 
"requested audience".
Mike Jones then made us aware of the work on resource indicators, but 
upon closer examination I found the "resource" parameter to be more 
limited than the "req_aud", since resource specifically states:

"Its value MUST be an absolute URI ... the "resource" parameter URI 
value is an identifier representing the identity of the resource"

My interpretation of this is that "resource" refers to a single 
resource, which is more constrained than the definition of the "aud" 
claim from 7519, which uses a StringOrURI value.  For example my intent 
was to use "aud" and "req_aud" for group identifiers 
("temperatureSensorGroup4711") and other non-uri strings 
(hash-of-public-key), which I cannot do with "resource".  We therefore 
decided to keep the "req_aud" parameter in draft-ietf-ace-oauth-params, 
even though is clearly overlaps with "resource".

Any comments and suggestions about that line of reasoning (especially 
from the OAuth point of view) are very welcome.

/Ludwig


-- 
Ludwig Seitz, PhD
Security Lab, RISE
Phone [phone]