Hey Angerag,
The reason surfing works in counterstrike is due to air acceleration and a bug that makes the engine think the player is in the air (no ground friction or braking applied) when it is on an incline at a certain speed.
I was able to implement source style air acceleration and ramplsliding via blueprint which is the basis for surfing, but you would need to tweak the logic for determining when the player can slide to enable full surfing