def _ensure_token(self):
        """Ensures we have a valid access token."""
        if self._authorization_headers is None:
            token = self._get_access_token()
            self._authorization_headers = {"Authorization": f"Bearer {token}"}
Ensures we have a valid access token.
llama-index-integrations/readers/llama-index-readers-microsoft-outlook-emails/llama_index/readers/microsoft_outlook_emails/base.py