I'm generally OK with the change, though it does change One problem I
have with this is that it can give a false sense of security about the
information being sent to the token endpoint and how trustworthy it is.
A client_id is public knowledge, and so someone impersonating a client
on the Authentication Endpoint could also impersonate it on the Token
Endpoint just as easily. This is not the attack that's being addressed
here, and the possible phishing vector in the one I'm describing is both
well known and, I believe, well covered by the existing documents.
However, I think the new text might confuse people into conflating these
two.
Basically, I think it needs to be made very clear, especially with this
change of text, that a client_id on its own should never be taken as
sufficient for authentication of the client. The context of the user's
decision, among other things, is as important as a client secret.
-- Justin
On 07/02/2012 11:17 AM, Mike Jones wrote:
I believe we should adopt this revised text.
-- Mike
*From:*[email protected] [mailto:[email protected]] *On
Behalf Of *John Bradley
*Sent:* Sunday, July 01, 2012 2:22 PM
*To:* [email protected] WG
*Subject:* [OAUTH-WG] New Text for Sec 3.2.1 & 4.1.3
Sec 4.1.2 states:
The authorization code is bound to the client identifier and redirection URI.
The security concern Sec 10.5 states
If the client can be authenticated, the authorization servers MUST
authenticate the client and ensure that the authorization code was
issued to the same client.
Sec 3.2.1
A public client that was not issued a client password MAY use the
"client_id" request parameter to identify itself when sending
requests to the token endpoint (e.g. for the purpose of providing
end-user context, client usage statistics).
Nothing in the current spec requires that a Public client send it's client_id or redirect_uri to the token endpoint.
The client _id is only sent if it is a confidential client capable of
authenticating itself.
The redirect_uri is only sent if the 'redirect_uri' parameter was included in
the authorization request.
If the client has one registered redirect_uri it would not be sent to the
authorization or token endpoint.
This leaves us with public clients using code flow that cannot determine if a token was granted to them or some other public client.
I propose changing Sec 3.2.1 to read:
A public client that was not issued a client password MUST use the
"client_id" request parameter to identify itself when sending
requests to the token endpoint. This allows the authorization server
to ensure that the code was issued to the same client.
Sending "client_id" prevents the client from
inadvertently accepting a code intended for a client with a different
"client_id".
Also change Sec 4.1.3 from:
o authenticate the client if client authentication is included and
ensure the authorization code was issued to the authenticated
client,
To:
o authenticate the client if client authentication is included,
o ensure the authorization code was issued to the authenticated
confidential client or to the public client identified by the
'client_id',
The Original text implies that it is a good idea to send it, but is unclear on
what security it provides.
It is a small change that should not brake existing implementations, but will
increase security for public clients using the code flow.
Regards
John B.
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