Configurable refresh token age when refresh_expires_in is not set.

[DavidTHoy]

Hello Aborn,

Thanks for all of the work here.

My provider returns the refresh_token, but unfortunately does not return the token refresh_expires_in date. I would like to add a feature to allow for the refresh token to still be set if there is no refresh_expires_in in the response.

Please let me know if there needs to be change for this PR to be approved. Thanks