Oauth refresh token (with PKCE)

     ┌───┐                            ┌────┐
     │app│                            │auth│
     └─┬─┘                            └──┬─┘
       │ POST /token form_ecoded         │
       │ grant_type=refresh_token&       │
       │ refresh_token={refresh_token}&  │
       │ client_id={client_id}           │
       │────────────────────────────────>│
       │                                 │
     ┌─┴─┐                            ┌──┴─┐
     │app│                            │auth│
     └───┘                            └────┘