I have created a trigger that validates user input against a web service after insert/update. Originally, I wanted to show a validation error on the data entry screen, but this is not possible due to
@Future methods not being supported in triggers.
I know that I could create a new lightning component to handle this validation, but would prefer not to. The preference would be to continue to leverage the native LEX UI, and instead notify the user via a popup, update in the notification area (in the top right corner), or a toast message. Is this possible? If not possible, what is the path of least resistance/lowest customization?