[Openid-specs-ab] Securing token requests when discovery service is used

Preibisch, Sascha H Sascha.Preibisch at ca.com
Sat Oct 31 04:54:36 UTC 2015

Yes Mike,

For the implicit flow there would be no /token endpoint. But if I am not mistaken the discussion was all about the code flow.

I think the main goal should be a solution that stops the flow when a client requests an authorization code and not when exchanging it for the access_token. And a solution should also not depend on a client doing various validations.


From: Torsten Lodderstedt <torsten at lodderstedt.net<mailto:torsten at lodderstedt.net>>
Date: Friday, October 30, 2015 at 2:36 PM
To: Mike Jones <Michael.Jones at microsoft.com<mailto:Michael.Jones at microsoft.com>>
Cc: Sascha Preibisch <sascha.preibisch at ca.com<mailto:sascha.preibisch at ca.com>>, "openid-specs-ab at lists.openid.net<mailto:openid-specs-ab at lists.openid.net>" <openid-specs-ab at lists.openid.net<mailto:openid-specs-ab at lists.openid.net>>
Subject: Re: [Openid-specs-ab] Securing token requests when discovery service is used

Hi Mike,

is the attack applicable for the implicit grant? I think it would require the attacker to proxy the legitimate OP's authz endpoint, which results in a different URL being displayed in the user agent.

kind regards,

Am 30.10.2015 um 21:14 schrieb Mike Jones <Michael.Jones at microsoft.com<mailto:Michael.Jones at microsoft.com>>:

The other thing that can't be faked by an attacker is the OP's keys. If the ID token isn't signed by the right keys, then the RP knows that there's a problem.  This points to a possible solution involving authenticating the jwks_uri value.

Remember also that the Implicit flows don't use a token endpoint. So solutions that involve authenticating the token endpoint won't work for deployments using only Implicit flows.

John, Justin, and Nov, when you send in your IIW session notes, can you also please send them here?

-- Mike
From: Preibisch, Sascha H<mailto:Sascha.Preibisch at ca.com>
Sent: ?10/?30/?2015 1:00 PM
To: openid-specs-ab at lists.openid.net<mailto:openid-specs-ab at lists.openid.net>
Subject: [Openid-specs-ab] Securing token requests when discovery service is used


Now that IIW is over I would like to bring up my thoughts regarding the
session we had with John regarding the discovery service issue.

If I am the 'bad' discovery service provider I can fake all values within
the discovery response. Except for the /token endpoint. That has to point
to my system in order for me to receive the authorization_code and client

Therefore I believe there are two solutions:

* the discovery response to the client has to include a secret which has to be included
in the initial /authorize request. The authorization server validates the
value and fails the request if it is invalid. This of course has the
drawback that the authorization server has to keep state. As a server guy
I would not like to support this flow

* The better solution I see, and as I mentioned during the discussion, is
that the client should include the target /token endpoint as an additional
request parameter for the initial /authorize request. The authorization
server does a simple string comparison and fails if the /token endpoint is
not the one as expected

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