Halo 5's armor unlocks

There are already dozens of threads about how H5 armor should look, but how should it be unlocked? By achievements? By a system like in reach? By ranks?

Like halo 3 !!!

Probably it’s own system or like reach and 3

I think some combination would be good, like some unlocking for achievements or when you find terminals or when you get to a certain rank (nothing to high though, like the equivalent of H3’s lieutenant).

I think there should be a variety of ways to unlock armour. Some of them through achievements from current and past Halo games. Others through progress or time played. Why have just one method when you can have a nice variety?