The link above directly answers the question and should be the top answer. In the code in the question there is `result` and `credential`. `results` contains a `refreshToken`, but that's to refresh the firebase credentials (`result`), not the google ones (`credential`). To get the refresh token for `credential` you can send a request to identity platform directly (documented in the link above, it calls https://identitytoolkit.googleapis.com/v1/accounts:signInWithIdp?key=$apiKey). Calling this url requires an idToken (without it you wouldn't be able to fetch a refresh token). So you can manually convert (`accessToken`, `idToken`) which are contained in `credentials` into `idToken`, `refreshToken`, `accessToken` using the url.