Support for "refresh_token"

I didn't find this in docs, is there `refresh_token` support?

```
refresh_token
OPTIONAL. The refresh token used to obtain new access tokens
using the same end-user access grant as described in
Section 4.1.4. The authorization server SHOULD NOT issue a
refresh token when the access grant type is set to "none".
```

No file or test is named. Start by tracing the existing OAuth access-token grant and checking the authentication documentation for refresh_token; compare the current behavior with the requested flow and confirm whether support already exists. Done means the support question has a documented, tested answer or a clearly scoped implementation path.

Written by the indexing model from the issue text.