code: 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"]
docs: 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>