LoginManager.getInstance(this).registerCallback(object : LoginCallback {
override fun onCancel() { }
override fun onSuccess(exchangeToken: String) {
//todo: send the exchangeToken to your server
override fun onError(errorMessage: String) { }
fun onActivityResult(requestCode: Int, resultCode:Int, data: Intent?) {
LoginManager.getInstance(this).onActivityResult(requestCode, resultCode,
super.onActivityResult(requestCode, resultCode, data)