Re: [OAUTH-WG] Issue: 'username' parameter proposal

[Eran Hammer-Lahav <[e-mail]>]

I'm not aware of anyone arguing against this feature. The only issue is a full security review before we add it to the spec. If one of the security experts here can spend a few minutes to review this, we can move forward and add it to the draft.

EHL

From: Joseph Smarr [mailto:[e-mail]]
Sent: Tuesday, April 20, 2010 9:36 AM
To: Eran Hammer-Lahav
Cc: Evan Gilbert; OAuth WG
Subject: Re: [OAUTH-WG] Issue: 'username' parameter proposal

Just to add some more context from experience, this "two users getting mixed together" problem happens a lot in practice, esp. when you have a mix of server-side and client-side auth. For instance, we saw this in our Facebook Connect integration in Plaxo--normally the user connects and Plaxo stores their session key in our databases, so when the user returns and logs in as plaxo-user-123, we look it up and know that he's also facebook-user-456. But some of Facebook Connect's UI widgets just look at the browser cookies on facebook.com<http://facebook.com>, where facebook-user-789 may be currently logged in (happens all the time with shared computers at home). Thus we often had pages that pulled some Facebook info server-side (as facebook-user-456) and some client-side (as facebook-user-789) and it was very confusing and potentially harmful (e.g. easy to accidentally post a story to the wrong account). The solution would be for Plaxo to be able to pass facebook-user-456 down to the JavaScript library, so it wouldn't just "silently auth" as a different user--presumably, it would just treat it as if no one was logged into facebook, if the passed-in user is not logged in. I think this is what Evan is proposing we enable for OAuth, especially if we want it to work client-side with immediate-mode (which I think we do).

Another related example of this problem we saw was with our photo-uploader plug-in inside Picasa Desktop for sharing photos on Plaxo. During the upload flow, it embeds a web browser, which lets you log in as plaxo-user-123, but when it's done uploading, it opens a default web browser, where you might be logged in as plaxo-user-456, leading again to a confusing mix-up of identities. We solved this by appending the session-info of the user from the embedded web browser on the URL of the main browser that gets opened, so it can clobber the session as needed and maintain continuity of session.

Hope these experiences provide some useful and concrete context for evaluating whether/how to support a username parameter in OAuth.

Thanks, js
On Tue, Apr 20, 2010 at 8:08 AM, Eran Hammer-Lahav <[e-mail]<mailto:[e-mail]>> wrote:
This attack is why the flow requires the client to present the callback it used again when getting the token.

EHL


From: Evan Gilbert [mailto:[e-mail]<mailto:[e-mail]>]
Sent: Monday, April 19, 2010 5:17 PM

To: Eran Hammer-Lahav
Cc: OAuth WG
Subject: Re: [OAUTH-WG] Issue: 'username' parameter proposal


On Mon, Apr 19, 2010 at 10:58 AM, Eran Hammer-Lahav <[e-mail]<mailto:[e-mail]>> wrote:
Thanks. That makes sense.

My concern is that the client will ask for a specific username but an attacker will change that request before it hits the server. The server then asks the (wrong) user to authenticate and returns a token. The client has no way of knowing it got an access token for the wrong user. Does requiring that the server returns the token with the username solves this? Is this a real issue?

This particular attack wasn't of concern to me, for a few of reasons:
- The request is HTTPS, hard to modify the request before it hits the server
- There are probably other, more dangerous attacks if you can modify request parameters (for example, you can modify the client_id and get the user to authorize the wrong app)

I'm willing to be convinced otherwise

I have no objections to this proposal but wanted to see some discussion and support from others before adding it to the spec.

EHL

From: Evan Gilbert [mailto:[e-mail]<mailto:[e-mail]>]
Sent: Monday, April 19, 2010 10:06 AM
To: Eran Hammer-Lahav
Cc: OAuth WG

Subject: Re: [OAUTH-WG] Issue: 'username' parameter proposal

User 1 is logged into Client site
User 2 is logged into IDP site

This can happen quite frequently, as client sites often have long-lived cookies and may only be visited by one user on a shared computer.

Right now client site has no way to ask for a token for User 1, and end result will be that User 1 starts seeing User 2's data.

On Mon, Apr 19, 2010 at 8:37 AM, Eran Hammer-Lahav <[e-mail]<mailto:[e-mail]>> wrote:
How can they both be logged in? I have never seen a case where two users can be both logged into to the same service at the same time...

EHL



On 4/19/10 8:33 AM, "Evan Gilbert" <[e-mail]<http://[e-mail]>> wrote:
More details on this enhancement.

Goal: Make sure you get an access token for the right user in immediate mode.

Use case where we have problems if we don't have username parameter:

 1.  Bob is logged into a web site as [e-mail]<http://[e-mail]>.
 2.  Mary (his wife) is logged into IDP on the same computer as [e-mail]<http://[e-mail]>
 3.  A request is made to get an access token via the User-Agent flow in immediate mode (or with any redirect without prompting the user)
 4.  -ob now has an access token for Mary and (posts activities, schedules events, gets contacts) as Mary
 5.  Hilarity ensues

Secondary goal: Provide a hint for non-immediate mode

On Thu, Apr 15, 2010 at 11:55 AM, Eran Hammer-Lahav <[e-mail]<http://[e-mail]>> wrote:
Evan Gilbert proposed a 'username' request parameter to allow the client to
limit the end user to authenticate using the provided authorization server
identifier. The proposal has not been discussed or supported by others, and
has not received a security review.

Proposal: Obtain further discussion and support from others, as well as a
security review of the proposal. Otherwise, do nothing.

EHL

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