Secure possession while in contact with the base is all that we are looking for on a play like this. It is not like a fly ball that is sno-coned. Unlike the fly ball, secure possession with the bare hand doesn't require the ball to not be touching the ground because it can be easily determined just by looking at it. It is also completely different than the ball on the ground and the glove over the top of it.
Just the palm touching the ball without the fingers around it, is not possession. Think of it this way... If you were to not change the grip and the fielder would lift their hand would the ball come up with the hand? If yes, you have possession. If not, you do not have possession. It is kind of like porn... you will know it when you see it.