-----Original Message-----
From: Torsten Lodderstedt [mailto:tors...@lodderstedt.net]
Sent: Saturday, September 11, 2010 1:01 AM
To: Eran Hammer-Lahav
Cc: Freeman, Tim; oauth@ietf.org
Subject: Re: [OAUTH-WG] Why give the redirect URI when trading an access
code for an access token?
Doesn't step 7 require the evil user to know the client's secret?
Am 10.09.2010 17:06, schrieb Eran Hammer-Lahav:
1. Evil user starts the OAuth flow on the client using the web-server flow.
2. Client redirects the evil user to the authorization server, including state
information about the evil user account on the client.
3. Evil user takes the authorization endpoint URI and changes the
redirection to its own site.
4. Evil user tricks victim user to click on the link and authorize access
(phishing or other social engineering attack).
5. Victim user thinking this is a valid authorization request, authorizes
access.
6. Authorization server sends victim user back to the client, but since the
redirection URI was changed, back to the evil user site.
7. Evil user grabs the code and exchanges it for an access token.
By checking that the callback URI used to deliver the code is the same as
the one used to initiate the flow, the authorization server can verify that the
user who initiated the flow is the same one to authorize access and finish the
flow.
EHL
-----Original Message-----
From: oauth-boun...@ietf.org [mailto:oauth-boun...@ietf.org] On
Behalf Of Freeman, Tim
Sent: Wednesday, September 08, 2010 8:05 PM
To: oauth@ietf.org
Subject: [OAUTH-WG] Why give the redirect URI when trading an access
code for an access token?
Hi. I'm new here. I searched the archives a bit and didn't
immediately find an answer to my question below. My apologies if
there was some previous discussion of this that I missed.
Looking at the draft spec at
http://tools.ietf.org/html/draft-ietf-oauth-v2-10,
I see in section 4.1.1 "Authorization code" on page 22 that it is
required to give the redirect_uri of the original request when
exchanging an authorization code for an access token, and the
authorization server must verify that the redirection URI is correct as well
as the authorization code.
Based on section 4.2 "Access Token Response" on page 25, it seems
that the redirect_uri is not used when constructing the response from
the authorization server.
So far as I can tell, the redirect_uri is useless in this request.
It does not contain any secrets. The authorization code is verified
and is meant to be an arbitrary unguessable identifier, so little is
gained by verifying the redirect_uri also. It is not used to construct the
reply. Why is it required?
Tim Freeman
Email: tim.free...@hp.com
Desk in Palo Alto: (650) 857-2581
Home: (408) 774-1298
Cell: (408) 348-7536
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