Apps that allow users to log in over a 3rd party authentication provider (e.g. Facebook, Google, Twoitter,...) should open a browser window to let the user authenticate against the provider. That means, at some point, an app is backgrounded and the user interacts with a browser window. Just before the browser opens, it's a recommended pratctice to inform the user about what will happen (see e.g. Getting Started with OAuth 2.0 - O'Reilly), let's say an alert window with something like "you will leave now the XYZ app and a browser window will open where you can enter your credentials safely".

My question: How can that be done if I use the facebook SDK for ios? Looking at the SDK, there seem to be no notifications and no designated states that would allow me to detect that the sdk is about to background my app and about to opening either Safari or the Facebook app.