Bypass caching when a cookie matching a pattern is present

The CACHE::disable command should work from HTTP_REQUEST to prevent the response being returned from cache, however to make doubly sure, try setting it from HTTP_RESPONSE as well (to ensure your response doesn't get cached). Also add in some debugging statements;-

when CACHE_REQUEST {
   log local0. "[HTTP::uri]"
}
when HTTP_REQUEST {
  set fDisable 0
  set c_cookies [HTTP::cookie names]
  set uri [HTTP::uri]
  if {[lsearch -regexp $c_cookies "SESS*"]} {
    set fDisable 1
    CACHE::disable
  }
}
CACHE_RESPONSE {
when CACHE_REQUEST {
   log local0. "[HTTP::uri]"
}
}
when HTTP_RESPONSE {
  if {$fDisable} {
    CACHE::disable
  }
}

Hopefully this helps solve your problem.