Cookies [1 ] - a package to provide parsing and formatting of HTTP cookies according to rfc2109 (with a nod to Netscape.) This package is part of Wub, and may be fetched from the above URL in its latest state.
As part of Wub, it's of course skewed toward server implementation, but I believe there are hooks and facilities for clients too.
A side note: cookies are implemented above to a fairly old standard. If you dig back far enough in the history you'll find an implementation up to the most modern standard. Unfortunately, however, there's substantial and almost irreconcilable differences between the major browser families' implementations such that this hoary old standard is the GCD of them all. Sad, really, but you know what they say about standards.