Two alien fleets battle in orbit. The winners attack earth and take resources to repair, but leave

[Nyxt]

Two alien fleets battle in orbit. The winners attack earth and take resources to repair, but leave a partially completed ship (in Australia if I remember right) that we complete and use to start exploring.
The aliens find out we are using their ship and technology and make a deal that we can keep it as long as we loosely work for them and follow their rules.
I found this as an ebook on the kindle store in either late 2015 or 2016.