NFS with Kerberos

Hello,

I have two questions about NFS with Kerberos authentication.

First, how can a user execute a cron job or an at job? The user is not
authenticated at the time when the job must be executed, so how can he
be authenticated and how can he access his home directory?

Second, how can NFS with Kerberos and SSH authorized_keys be combined?
The user has to be authenticated (so must enter a password) for
authorized_keys to be read, but the purpose of authorized_keys is
obviously to login without a password.

Regards
  Christoph