John in the tower and NordicLight are correct . It is surprising that OSL doesn't give any information about DOM-INT-connections at all, but it is very easy (even if a longish walk). I do this regularly myself.

45 minutes is usually sufficient on SK DOM-OSL-INT, but count on spending 15 of them walking. Luggage will be tagged through, and you will not see it until you reach BCN. Just follow the sign to transfers. Be aware that the official connection point (where transfer security check as performed many years ago) is halfway down the domestic pier, so you'll have to do a bit of backtracking. There are temporary unmarked stairs down to the first floor domestic departure lounge before coming to the official connection point, if you pass one, just use it. From the domestic departure lounge follow the sign to the international departure lounge on the same floor, (through the one-way doors into the tax free shop)

Be aware that in some cases (dual INT/DOM gates, bus gates) you will end up before the one-way doors into the luggage hall on the ground floor. DO NOT go through them. Follow the sign up the very long flight of the stairs to the second floor and then the sign to the transfer check point, or use the elevator (somewhat hidden).

On a through flight SAS knows that you are coming, and there probably are quite a number of other PAX connecting to other flights as well. Just walk quickly to the departure gate.

I prefer to have a slightly longer connection if possible, especially in winter, to visit the lounge. But not if having to catch the 06.35 flight instead of the 09.20 for instance.