Oauth refresh token (with PKCE)       
                                                  
     ┌──────────┐                    ┌───────────┐
     │mobile app│                    │Auth server│
     └─────┬────┘                    └─────┬─────┘
           │POST /token form_ecoded        │      
           │grant_type=refresh_token&      │      
           │refresh_token={refresh_token}& │      
           │client_id={client_id}          │      
           │──────────────────────────────>│      
     ┌─────┴────┐                    ┌─────┴─────┐
     │mobile app│                    │Auth server│
     └──────────┘                    └───────────┘