The user-agent security is based on the presence of the end-user. This is important. It is not like a client with the same ID can just go and ask for an access token (if one was previously approved). The end-user must be present. How the end-user presence is verified is something each server has to figure out.
EHL On 7/3/10 12:12 PM, "Andrew Arnott" <andrewarn...@gmail.com> wrote: On Fri, Jul 2, 2010 at 9:12 PM, Eran Hammer-Lahav <e...@hueniverse.com> wrote: You are putting too much weight on the value of redirection URI registration. Since the same problem exists between the user-agent script and the server-side component used in the user-agent profile, anyone can imitate that flow. In most cases, the redirection URI will simply include a script that will pass the parameter to the *parent* window which can be anything. If the server-based page is an active page, it still needs to communicate with the user-agent, which again, can pretend to be that. Good point. I wasn't imagining that far through it. Not to deny that most redirection URLs may just return a straight script that passes it to the parent window, but that seems pretty irresponsible to the host that's doing it -- because of the enormous security hole it opens up. Some client is trusted enough to authorize (by the user and auth server), receives an access token it wasn't expecting, and then blindly forwards it onto whoever wants it. Yikes. I sure hope these access tokens have very limited scope (like, I'd prefer none myself). I was about to describe how an active server could alleviate that by signing the original request using the state parameter, but I realized I'm solving a problem that the web server flow (or nowadays that the authorization code mode as I guess it's called) already solves. So I guess I just need to bite the bullet and accept that the user agent flow is totally insecure for web clients, and thus very special care must be taken to enable native clients without opening up the web client hole. Sorry to sound so negative about it. Enabling this scenario seems really important to me as well -- I just am against doing it when it can't be secured in some way. Seriously... as is, once you authorize any client, you've authorized them all, including clients not even running on your computer. I guess this answers how I was visiting a site a few days ago and was amazed that it knew who I was (via Facebook) and was displaying my name and photo when I never logged into the site. I was shocked it knew who I was. Enter living in Incognito mode from now on.
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