So the '@' here was there before I got there, but it doesn't work. My only change to this line is to add an escape to the '.' so that it is a literal dot instead of a regex dot, which as I understand it, would match anything.

I'm not really sure what this line and the line below it do, what I do know is that they don't allow '@' symbols in host/cert names, despite the content of the comment to the right. However, they must do something, because if you change line 273 to munge_name(value) instead of [value], certs with '@' symbols start working and a bunch of tests in authstore_spec start to fail.