What is the full curl command to get access token with request token?

Hi,
The sample in this repo is pretty straightforward and clear. Thanks.

One thing is not mentioned in tutorial is getting new access_token with refresh_token as way of renewing an access_token.

I tried below command and the other which had auth tuple and both failed.

```sh
$ curl -XPOST http://127.0.0.1:8000/oauth/token -F grant_type=refresh_token -F refresh_token=NogJYgBFjH3NmTBDHdDYTCUQBQaMXBFZThdjaHtjraEuT9HM
{"error": "invalid_client"}
```

The other test is adding client_id and cilent_secret:
```sh
curl -u ${client_id}:${client_secret} -XPOST http://127.0.0.1:8000/oauth/token -F grant_type=refresh_token -F scope=profile -F refresh_token=${refresh_token}
{"error": "unauthorized_client"}
```

What is the correct curl command to get access token with refresh token?

Thanks

Esamina il tutorial OAuth del repository e le richieste /oauth/token mostrate nell’issue, iniziando dal flusso refresh_token. Conferma il formato di richiesta supportato e aggiorna il tutorial con un comando curl funzionante; il lavoro sarà completato quando i passaggi per il rinnovo del refresh-token e i parametri richiesti saranno documentati chiaramente.

Scritto dal modello di indicizzazione a partire dal testo della issue.