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From: John Bradley <ve7jtb@ve7jtb.com>
In-Reply-To: <54DA154C.2070700@redhat.com>
Date: Tue, 10 Feb 2015 11:49:33 -0300
Message-Id: <9F3B04D0-3BE6-4AFD-ADA0-91137B023864@ve7jtb.com>
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To: Bill Burke <bburke@redhat.com>
Archived-At: <http://mailarchive.ietf.org/arch/msg/oauth/AmNpMFPbIMa3Jt7fmpVJjRkW0bA>
Cc: oauth@ietf.org
Subject: Re: [OAUTH-WG] Confusion on Implicit Grant flow
Precedence: list


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The nonce allows the client to insert a unique value into the id_token  =
to associate it with a particular browser session(Think SAML RequstID).  =
=20
That is useful for web server based clients.  It may or may not be =
useful in the JS case, as the client is the browser.

While code can only be used once, that doesn't stop someone from  =
intercepting a code/id_token from one session and replaying it in a =
different one to the same client.  =20

In the JS client case that would require a man in the middle between the =
browser and the AS, so is much harder for an attacker than the case =
where the client is a web server.

Using the PKCE code_challenge also lets the client detect if some =
substitution of the code has happened.

John B.
> On Feb 10, 2015, at 11:27 AM, Bill Burke <bburke@redhat.com> wrote:
>=20
>=20
>=20
> On 2/10/2015 8:15 AM, John Bradley wrote:
>> The issue is maintaining key material in the browser.
>>=20
>> Web Crypto will help with that , but is not deployed widely in =
browsers at the moment.
>>=20
>> Thinking about it a bit someone could make a more secure flow for JS =
clients using code and some Connect extensions now.
>>=20
>> If I were concerned about logging the AT, then I would have the JS =
make a CORS call to the authorization endpoint with:
>> response_type=3Dcode+id_token              =
[http://openid.net/specs/oauth-v2-multiple-response-types-1_0.html]
>> code_challenge=3D(challenge value)        [ =
https://tools.ietf.org/html/draft-ietf-oauth-spop-02]
>> code_challenge_method=3DS256
>>=20
>=20
> Excellent.  Thanks.
>=20
>=20
>> In Connect the JS client crates a nonce value and sends that with the =
request.  That value comes back in the signed_id token allowing the JS =
to know that the code and id_token are in reply to it's request and not =
replayed from another session.
>>=20
>=20
> Why would you need the nonce if the IDP guarantees that the code can =
only be used once?  The code, state, and redirect-uri are all validated =
by the IDP with the access token request.
>=20
> Bill
>=20
> --=20
> Bill Burke
> JBoss, a division of Red Hat
> http://bill.burkecentral.com
>=20
> _______________________________________________
> OAuth mailing list
> OAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/oauth


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