Attempt Access Token refreshment before forwarding the request if expired

After OPENIG-933 we'll have a mechanism for reacting to UNAUTHORIZED messages from the resource server.

It's the more standard way of doing that, but it comes with a price: 3 HTTP calls: RS failure, token refresh and RS redo.

It's possible to do it more efficiently if the access token contains an expiration time: we could test token expiration and do the refresh before calling the RS: 2 calls instead of 3.