According with Microsoft,
Will it affect K2?
Seeing as this was posted in K2 blackpearl forum, I assume you're still on K2 4.7 or below.
There's still about 2 years before the date stipulated for the Microsoft change to take effect. But K2 4.7 will reach its end of life before that at the end of 2019 (http://help.k2.com/k2compatibilitysupportmatrix). What this means is that it is possible that there may not be an update for 4.7 to address this change in authentication behaviour.
So to be safe, if you're still on 4.7 or below, do plan to upgrade to the latest version (currently 5.1) to ensure you are eligible for the latest fix releases.