I'm busy to enable login stuff via facebook oauth on my website, but the only thing I want to get is the email of the user.
I saw in dev docs the 'scope=email' but, it seem's mandatory for the user to allow access to anything about him.
is there's a way to ask him to grant access only on his email ?
No. The bare minimum that your app will request from the user is his Basic Information, followed by your extended permissions (in your case, his email address).