To furhter qualify Justin's suggestion, you can write
user_id's directly into the access log without
having to "massage cookies". Like Justin said,
you would put something like this in your server config file:
ns_param ExtendedHeaders X-User-Id
And then you would have to make sure the following code gets
run on every request, before you serve the page.
ns_set put [ns_conn headers] X-User-Id "user_id=$user_id"
