At the moment I'm also still very new to Laravel. But as far as my knowledge goes, middleware would be the perfect way to add this functionality to your application? It would require a view that can be accessed both by GET as by POST. Add the middleware to protected routes and check a "last activity" session, if the time passed is greater than X (you decide the time) display the "lockscreen" view, otherwise you simpley do the following to proceed to the next step.
return $next($request);
Simplified, this is what the middleware should do:
public function handle($request, Closure $next)
{
if ( time() - Session::get('last_activity') >= 600 ) {
return redirect('lockscreen');
}
return $next($request);
}
The example in the docs (https://laravel.com/docs/master/middleware) should push you in the right direction.