Configuring preauth

[Jeff Blaine]

MIT Kerberos 1.8, all Linux for now, custom build

It's my understanding that the existence of a preauth
module in lib/krb5/plugins makes the module required.

Is that correct?  I bet it's not, and if so, I would
love to have someone explain what reality is.

Is there any documentation on configuring preauth at
all?  I already found +require_preauth as part of
addprinc/modprinc

Thanks for any help!