in uber-core/src/main/java/com/uber/sdk/core/auth/AccessTokenAuthenticator.java [91:99]
protected synchronized Request doRefresh(Response response) throws IOException {
final AccessToken token = tokenStorage.getAccessToken();
if (signedByOldToken(response, token)) {
return resign(response, token);
} else {
return refreshAndSign(response, token);
}
}