3.2.5.1.2.1.3 Refresh Token Authentication
If authenticating the user by using a previously obtained refresh token, the client includes the following fields in the JWT described in section 3.2.5.1.2.1:
grant_type (REQUIRED): "refresh_token"
refresh_token (REQUIRED): A refresh token ([RFC6749] section 1.5) that was previously obtained from the server.