Spec compliance: invalid_request returned when refresh token invalid

[jacobweber]

According to the OAuth2 spec, when you're using the refresh_token grant and the refresh token has expired, it should return an invalid_grant error. But this server actually returns a invalid_request error.

       invalid_grant
              The provided authorization grant (e.g., authorization
              code, resource owner credentials) or refresh token is
              invalid, expired, revoked, does not match the redirection
              URI used in the authorization request, or was issued to
              another client.

[Sephster]

Well spotted. Thanks for finding this issue @jacobweber

[Sephster]

Fixed in PR #1042