Just bumped into the same issue. I was able to solve it by storing the token expiration time next to the accessToken itself (auth0-java-1.13.3):
TokenHolder tokenHolder = authAPI.requestToken("https://" + AUTH0_DOMAIN + "/api/v2/")
.execute();
String accessToken = tokenHolder.getAccessToken();
long accessTokenExpiresIn = tokenHolder.getExpiresIn();
With that in place one can trigger a refresh (or get a new) token before the existing one expires before an actual API call.