How to get Flight Training (and an according rating) during the TNG era for persons who did not want to join Starfleet but were inhabitant of a planet within the Federation?
We have, as an example, Kasidy Yates(-Sisko). In her biography on Memory Alpha, it is not mentioned with any word that she was part of Starfleet at any point. Nontheless, she was allowed to operate for Starfleet and in their controlled space. On the other hand, it would be too dangerous to let anybody without any training take control over a Warp capable ship.
So, how was it determined who's allowed to fly a Warp capable ship in Federation space and where was it possible to get the necessary ratings?