You need to be registered as a drone operator in an EU country or Norway. You should register in the first country where you plan to operate. For Norway, you can register at Norwegian website flydrone.no (they have an English version).
This is also valid for sub-250g drones that has a camera and is not marked as a toy.
You also need a liability insurance.
Flying over the city Oslo is forbidden.
And never ever fly within 5 km from an airport. Norway is very strict on that, and has very advanced detection systems. You will be fined around $1000, lose your drone and risk being deported from the country!
Otherwise flying in Norway is quite relaxed. 120 meters max height, no flying in national parks.