Get the application's access token as a string.
        If offline=True, use the concatenated app ID and secret
        instead of making an API call.
        <https://developers.facebook.com/docs/facebook-login/
        access-tokens#apptokens>

def get_app_access_token(self, app_id, app_secret, offline=False):
        """
        Get the application's access token as a string.
        If offline=True, use the concatenated app ID and secret
        instead of making an API call.
        <https://developers.facebook.com/docs/facebook-login/
        access-tokens#apptokens>
        """
        if offline:
            return "{0}|{1}".format(app_id, app_secret)
        else:
            args = {
                "grant_type": "client_credentials",
                "client_id": app_id,
                "client_secret": app_secret,
            }

            return self.request(
                "{0}/oauth/access_token".format(self.version), args=args
            )["access_token"]