Canvas -> LPE -> Alpha Mask ?

cgidesign

Situation:

Let`s say two individual clothing items are layered on top of each other.

The top one 'Cloth A' uses an opacity mask in the material.

I now like to output a canvas that contains the opacity information of 'ClotH A'. This alpha mask I like to use for compositing in an image editor. Therefore I only need the alpha but not lighting like glossy etc.

Does anybody have a LPE example for me to achive this?

I tried all examples I found online but all created a fully black exr in the end.