def METHOD_NAME(self, code: str) -> str | None:
    """Complete the web authorization flow and return the refresh token.
    :param code: The code obtained through the request to the redirect uri.
    :returns: The obtained refresh token, if available, otherwise ``None``.
    The session's active authorization will be updated upon success.
    """
    authenticator = self._reddit._read_only_core._authorizer._authenticator
    authorizer = Authorizer(authenticator)
    authorizer.METHOD_NAME(code)
    authorized_session = session(authorizer)
    self._reddit._core = self._reddit._authorized_core = authorized_session
    return authorizer.refresh_token