[mitreid-connect] Introspection endpoint - scopes check

[Justin Richer]

The rationale behind this functionality is that you don't want to 
inadvertently leak information to a protected resource about the overall 
reach of a token if the token is usable beyond that particular protected 
resource. Let's say I have two resources, "A" and "B", and they have 
associated scopes, "a" and "b". If the client gets a token with scope "a 
b" and plays it at "A", we might not want "A" to inadvertently discover 
that the token could also be used at "B".

I would not recommend removing the check entirely, /however/: the 
behavior has changed in version *1.2.0* such that the server doesn't 
return an error anymore, but instead returns only the scopes associated 
with the protected resource. In the scenario above, when "A" introspects 
the token with "a b", it gets back a response that only includes "a" in 
the scope field, while "B" would get back a response that only includes 
"b" in the scope field of the same token.

  -- Justin

On 8/27/2015 4:12 AM, Zaninetta Stefano wrote:
> Hello,
>
> I noticed that the Introspection endpoint is returning 403 if the 
> introspecting client configuration doesn't include all the scopes 
> associated with the introspected token.
> (https://github.com/mitreid-connect/OpenID-Connect-Java-Spring-Server/blob/mitreid-connect-1.1.15/openid-connect-server/src/main/java/org/mitre/oauth2/web/IntrospectionEndpoint.java#L130)
>
> I don't understand what is the reason of for that check and I couldn't 
> find such recommendation in the latest specs 
> (https://tools.ietf.org/html/draft-ietf-oauth-introspection-11).
> Could anyone explain me what is the rationale behind that?
>
> At the moment the workaround we adopted is to configure all the 
> available scopes for all the clients used by the Protected Resources; 
> that is equivalent to skip the check.
> Hence, I was considering removing it from the code, but I want to be 
> sure I'm not missing any security implication.
>
> Thanks a lot,
> Stefano
>
>
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