Password hash as LUKS key

Hey,

I want to encrypt drives for users. I want to avoid having their password sent to me in clear text. 
I was thinking of having them use a tool like mkpasswd to create a password hash and then 
pipe the generated hash into cryptsetup luksAddKey.

Unfortunately that didn't work when I tried it. 

So I guess it's not supported right? Maybe you know some other way to achieve what I want to accomplish?

BR,
Martin