Minus a level of indentation
Don't bother exposing the authenticator

First off, asciiAuthent is a lie. In krb5, it's Zcode. And the length isn't
really useful for anything. And we're not going to do anything useful with it
in JS anyway.
Allow swapping out the sender
Let you switch cert_routine to one of three options

A bit cumbersome though. Closes #3.