问题
Following up on the design outlined in Design for Facebook authentication in an iOS app that also accesses a secured web service, and specifically the concern listed in https://stackoverflow.com/a/12912616/5154090: what would be the mitigation?
Specifically, I have a web server that exposes a REST API which is consumed by a mobile app. I'd like users to authenticate to the server (via the app) using Facebook.
Now, an apparently common flow is for the app to redirect the user to Facebook, where they will login with their credentials. The app will then get a token which it will send to the server, and the server will validate the token using the graph API.
But how can the server make sure that the token really came from the app? Specifically, what's to prevent a malicious app vendor from re-using my app ID? After all, the app ID is hardcoded into the app and can therefore be extracted and used by a malicious app. If users log into that malicious app with Facebook, then the malicious vendor can get tokens with my app ID and can impersonate users of my service.
How can one protect against this?
回答1:
To summarize for anyone else who happens to contemplate this - there is indeed no way to prevent the client ID from being spoofed. This is one reason that developers are discouraged from using the OAuth implicit flow in native apps as pointed out by Andre D in https://stackoverflow.com/a/17439317/5154090:
the use of the Implicit Flow with native apps is NOT RECOMMENDED.
(see https://tools.ietf.org/html/draft-ietf-oauth-native-apps-09#section-8.5).
In practice, if anyone mounts this attack, then the user will download App A (a malicious app) and will then be asked to authorize App B to make actions on their behalf. As far as I can tell, this is generally the only indication that an attack is taking place.
来源：https://stackoverflow.com/questions/43304949/spoofing-facebook-app-id