I think that saying the "Trump administration gave the green light" is a bit of an interpretation on the part of the reporting journalist.
We know that the African mission has been on the Liberal's radar since they became the government in Canada as a a "re-join the UN so we can have a seat on the Security Council" plan. When it looked like Clinton would win, they knew that there would be little change in US policies, so they could plan accordingly. When Trump won, and considering the noise he made about not pulling our weight and about having a plan to defeat ISIL (even if we now know that his plan - the details of which he wouldn't reveal to keep the enemy guessing - consists only in now asking his appointees to come up with a new plan), it was normal to try and figure out what the US wanted to do.
Of course, you can't just go to the Americans and ask squarely "what are your plans". So you do it in reverse: You say "I was thinking of doing A-B-C, would that constitute a problem for you?" If they say "I don't see any problem." you are fine. On the other hand, if they say "Hummm! I, myself, was thinking of doing X-Y-Z and was hoping to ask you to take part" then you know where you stand.
Personally (and it is a personal opinion here) I believe that another aspect of the Liberals "asking" the US if it was OK is just another Liberal move driven by their cowardice in facing the nation with the truth now that they know that there is no "safe little mission" of happy blue helmets out there and there would be casualties. They were hoping to be able to renege on the basis of "We wanted to go, but the Americans won't let us".