"Cookies" are a user-facing computing construct. They are codified in many technical specifications, including the earliest reference in an HTTP spec, RFC 2109, published February 1997.
Many claim the use in HTTP followed from UNIX "magic cookies." Eric Raymond provided a definition of what a "magic cookie" is:
Something passed between routines or programs that enables the receiver to perform some operation; a capability ticket or opaque identifier [...]
But why did the UNIX community start using the phrase "cookie" to begin with? Is it because you put cookies into a jar, and take them out? When did this whole thing begin? Does anyone have a citation of the first usage?