Revoking Login

  You can also let people completely de-authorize an app, or revoke login, by making a call to this Graph API endpoint:

  DELETE /{user-id}/permissions

  This request must be made with a valid user access token or an app access token for the current app. If the request is successful, your app receives a response of true. If the call is successful, any user access token for the person will be invalidated and they will have to log in again. Because you're de-authorizing your app, they will also have to grant access to your app as if they were logging in for the first time.