Issue with Refresh Token Not Updating on Expiration via OAuth Endpoint

Hi,

We've encountered an issue with the expiration of the refresh token. According to the documentation, refresh tokens are valid for 6 months.

The documentation states:

> Repeat this process as necessary, ensuring you use the refresh token at least once before its 6-month expiration to obtain a new set of credentials without having to restart the OAuth process from step one.

However, when we use the `POST https://app.frontapp.com/oauth/token` endpoint to obtain a new pair of access and refresh tokens, we indeed receive a new valid access token (extended for 1 hour), but the refresh token remains unchanged, including its expiration.

As a result, we are unable to update the refresh token. How can we resolve this issue?

I am testing with the following refresh token:
- Issued At: 1699617655 (11/10/2023, 2:00:55 PM)
- Expiration Time: 1715342455 (5/10/2024, 3:00:55 PM)

And I received the same token back from the `POST https://app.frontapp.com/oauth/token` endpoint.