Ask HN: why were magic cookies so-called?

The immediate source of the name of HTTP cookies is that they were named after "magic cookies", a then-current CS term for a string of code used as an identifier (i.e. exactly like HTTP cookies). But where did that term come from?

Several people have suggested that "magic cookie" is a synonym for "fortune cookie", which seems reasonable, but I've not found any persuasive primary sources for that theory yet.

Help me out, nerds of HN!