'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):

    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']
