I have a Facebook Connect app that I monetize using Google AdSense. I want to be sure that I am not leaking any Facebook user information such as the Facebook UserID number or the access token (which has the UserID in it).
AdSense is perfectly legit and within Facebook policy for Connect applications. I just need to be sure Google cannot see the information that identifies the user.
I was well aware of these requirements when I designed my application, and thought I had it nailed, but then I received one of the famous automated warning emails from Facebook stating:
“Our automated systems have detected that you may be inadvertently allowing authentication data to be passed to 3rd parties.”
it also stated:
“In every case that we have examined, this information is passed via the HTTP Referer Header by the user’s browser.”
Again, I was already familiar with this leakage vector, which happens when Facebook puts the access token into the querystring when it redirects back to your app after user authentication. I already have a design in place where I handle this through server-side OAuth 2.0 redirection, obtaining a “code” and exchanging it for an access token. This method is described here, under server-side authentication: https://developers.facebook.com/docs/authentication/
In my app, I do the code-for-token exchange in a separate ASP.NET MVC controller that has no views, so there is no Adsense or any 3rd party resources included. So I am certain that all of my header referer field contents and querystrings are clean and contain no user data.
Given that I received the email notice from Facebook however, and don’t want my app and the AdSense money faucet turned off, I am now paranoid that there is some other place I am leaking data. Then again, the email says my app “may be” leaking information (why oh why can’t they just tell me what they saw, or at least be certain it is leaking rather than it just “may be” leaking), and it says every instance was due to the referer/querystring, which again I am certain (having done Fiddler tracing) my app is clean.
I see only one possible way the info could be leaking, but I’m not sure if it is a real risk or just a lack of understanding on my part of what exactly AdSense (and Google Analytics) can see from my app’s content on a page that requires the user to be authenticated.
I have a view (page) where I put the access token into a hidden form field. It is put there when the page is initially served up (after the user has been authenticated), and then subsequently updated via Javascript (using the Facebook JS SDK) so when the user posts the form back to the server, I get an updated access_token if it has changed. The access token can change because I use the Javascript SDK to prompt for additional permissions on that page, including in some cases the offline_access extended permission. Getting offline_access will generate a new access_token, one that does not expire.
This is on a page that requires the user to be authenticated to see it, so I figured AdSense cannot see the page contents. I do have the view setup to render in a generic fashion (no user info) with all of the same text if the user is not authenticated, but with the addition of a “login now” prompt, so Adsense can index the page and provide relevant contextual ads.
I am aware of the fact that Facebook just yesterday launched the new OAuth 2.0 Javascript SDK features, but can’t adopt that right away as it won’t work with the Facebook C# SDK I use server-side. And even with that, if I have a problem with putting the access token in the hidden form field, that problem would still be there.
In classic Facebook fashion, they give me 48 hours to fix the problem, but any inquiries via their developer support web form only result in a response that they will “do our best to respond to your specific issue within one week.”
Maybe a simpler way to think of this problem is “can Google AdSense see the page contents of a page requiring user authentication?” or do they only see the header referer field from which the AdSense javascript file was loaded.
They got back to me after a manual review of my site and said it was not actually leaking any user info. Gee thanks for the runaround Facebook automated detection systems!