how to stop Save in standard Object depending on response of a sync call

Hi, I am using Standard Lead layout and i have a requirement to call a Sync service and based on response of that service, allow or Stop the Lead to Save . The Problem is, i cannot call the sync service from Before insert trigger. What are my options ? if I create a lightning component and override Standard Save button, can i just add my additional logic and reuse rest of the standard save functionality ? Or shall i user a lightning component to Call the Sync service but then how do i stop the Save if required based on the response of the service.

Please help urgently.

Thanks