I have a Drupal 8 installation profile with custom modules and themes and I am wondering how should I use composer so that I can run it and drupal core and other dependencies(like contrib modules) would get properly downloaded(and also Drupal's cusom composer stuff would get properly applied as well)?

Is this possible at this time or the composer approach is still not complete?

I have an installation profile with custom modules and themes.

How should I use Composer so that Drupal and the installation profile's dependencies are downloaded and copied in the right directories?