After running
mix igniter.install ash_authentication_phonix
the book states: „Before we can test it out, there’s one manual change we need to make as Igniter doesn’t (yet) know how to patch JavaScript or CSS files.“
However, running the igniter actually inserts the line
@source “../../deps/ash_authentication_phoenix”;"
in app.css so one no longer needs to do that manually.
So I think Ash development might have overtaken the book here once more. 
