We're seeing that refreshing tokens from outside of a GCP env is slow, often around 1 second for us. Because of this we'd like to get the refresh done in background outside of the get_token call. This is possible but awkward currently as there's no direct way for a consumer to trigger refresh other than to call get_token in the last 20 seconds of the token lifetime.

Ideally the library would offer a background refresh option, or if not that, the ability to force a refresh.

I can put together a PR for either of these approaches if this is something you're interested in.