[mitreid-connect] Introspection endpoint - scopes check

[Zaninetta Stefano]

Thank you Justin for the explanation!
I'll consider upgrading to 1.2 or implement the same behaviour in our version!

Regards,
Stefano
________________________________
From: Justin Richer [jricher at mit.edu]
Sent: Thursday, August 27, 2015 12:48 PM
To: Zaninetta Stefano; mitreid-connect at mit.edu
Subject: Re: [mitreid-connect] Introspection endpoint - scopes check

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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