Re: [OAUTH-WG] OAuth 2.0 Discovery Location

George Fletcher <> Wed, 24 February 2016 19:17 UTC

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To: Phil Hunt <>, Nat Sakimura <>
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From: George Fletcher <>
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Date: Wed, 24 Feb 2016 14:17:05 -0500
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Subject: Re: [OAUTH-WG] OAuth 2.0 Discovery Location
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I'm concerned that forcing the AS to know about all RS's endpoints that 
will accept it's tokens creates a very brittle deployment architecture. 
What if a RS moves to a new endpoint? All clients would be required to 
get new tokens (if I understand correctly). And the RS move would have 
to coordinate with the AS to make sure all the timing is perfect in the 
switch over of endpoints.

I suspect a common deployment architecture today is that each RS 
requires one or more scopes to access it's resources. The client then 
asks the user to authorize a token with a requested list of scopes. The 
client can then send the token to the appropriate RS endpoint. The RS 
will not authorize access unless the token has the required scopes.

If the concern is that the client may accidentally send the token to a 
"bad" RS which will then replay the token, then I'd rather use a PoP 
mechanism because the point is that you want to ensure the correct 
client is presenting the token. Trying to ensure the client doesn't send 
the token to the wrong endpoint seems fraught with problems.


On 2/24/16 9:59 AM, Phil Hunt wrote:
> Nat,
> I’m not sure that having the resource server tell the client where its 
> authorization server is secure by itself. The relationship between the 
> Authorization Server and the Resource server need to be bound together 
> in one of the discovery endpoints (the resource and/or the oauth 
> service discovery).
> If a client discovers a fake resource server that is proxying for a 
> real resource server the current discovery spec will not lead the 
> client to understand it has the wrong resource server. Rather the fake 
> resource service will just have a fake discovery service. The hacker 
> can now intercept resource payload as well as tokens because they were 
> able to convince the client to use the legit authorization service but 
> use the token against the hackers proxy.
> The OAuth Discovery service needs to confirm to the client that the 
> server is able to issue tokens for a stated resource endpoint.
> This not only works in normal OAuth but should add security even to 
> UMA situations.
> Phil
> @independentid
> <>
> <>
>> On Feb 24, 2016, at 3:54 AM, Nat Sakimura < 
>> <>> wrote:
>> Hi Thomas,
>> inline:
>> 2016年2月22日(月) 18:44 Thomas Broyer < 
>> <>>:
>>     Couldn't the document only describe the metadata?
>>     I quite like the idea of draft-sakimura-oauth-meta if you really
>>     want to do discovery, and leave it open to implementers / to
>>     other specs to define a .well-known URL for "auto-configuration".
>>     The metadata described here would then either be used as-is, at
>>     any URL, returned as draft-sakimura-oauth-meta metadata at the
>>     RS; or as a basis for other metadata specs (like OpenID Connect).
>>     With draft-sakimura-oauth-meta's "duri" and the "scope" attribute
>>     of WWW-Authenticate response header, you have everything you need
>>     to proceed
>> Yup. That's one of the requirements to be RESTful, is it not?
>> In OAuth's case, the resource and the authorization server are 
>> usually tightly coupled. (Otherwise, you need another specs like UMA.)
>> So, the resource server should be able to tell either the location of 
>> the authz endpoint. In some trusted environment, the resource may as 
>> well return the location of the authz server configuration data. In 
>> these cases, you do not have to decide on what .well-known uri as you 
>> say. This frees up developers from configuration file location 
>> collisions etc. We should strive not to pollute the uri space as much 
>> as possible.
>>     (well, except if there are several ASs each with different
>>     scopes; sounds like an edge-case to me though; maybe RFC6750
>>     should instead be updated with such a parameter such that an RS
>>     could return several WWW-Authenticate: Bearer, each with its own
>>     "scope" and "duri" value?)
>> Yeah, I guess it is an edge case. I would rather like to see these 
>> authz servers to develop a trust framework under which they can agree 
>> on a single set of common scope parameter values.
>> Cheers,
>> Nat
>>     On Fri, Feb 19, 2016 at 10:59 PM Justin Richer <
>>     <>> wrote:
>>         The newly-trimmed OAuth Discovery document is helpful and
>>         moving in the right direction. It does, however, still have
>>         too many vestiges of its OpenID Connect origins. One issue in
>>         particular still really bothers me: the use of
>>         “/.well-known/openid-configuration” in the discovery portion.
>>         Is this an OAuth discovery document, or an OpenID Connect
>>         one? There is absolutely no compelling reason to tie the URL
>>         to the OIDC discovery mechanism.
>>         I propose that we use
>>         “/.well-known/oauth-authorization-server” as the default
>>         discovery location, and state that the document MAY also be
>>         reachable from “/.well-known/openid-configuration” if the
>>         server also provides OpenID Connect on the same domain. Other
>>         applications SHOULD use the same parameter names to describe
>>         OAuth endpoints and functions inside their service-specific
>>         discovery document.
>>          — Justin
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