I'm having trouble on showing again the Facebook authorization window, the one you choose which permissions you want to give to the application you're trying to access.
The first time you click on Facebook the window appears, but then you can choose not to share your email which is fine, however that is a requirement for our application.
If the user clicks again on the Facebook button the authorization window no longer appears, and the user cannot change what he initially selected.
I assume there is a way to re ask for permissions, or am I wrong?
I'm afraid you can't do that.
Facebook does it like that so that you don't get those annoying services requiring you to let them have full access of your account to see some cat funny videos.
If the user chose not to share his email address, then you need to deal with that and give the user the possibility to add an email on your application.
Another approach would be to inform the user that he needs to go to Facebook and manually change what he initially selected (More or less what iOS does with app permissions).