APM iRule Event: insert Cookie after Logon Page

You may need both, one to insert the cookie to the application server and the other to set the cookie back to the client browser. And some logic avoid the repeat.

when HTTP_REQUEST {
  set flag 0
  if { [HTTP::cookie MyCookie] ne "" }{
     set flag 1
  }
}

when ACCESS_ACL_ALLOWED {
  if { $flag eq 0 }{
     HTTP::cookie insert name "MyCookie" value "MyValue" path "/"
  }
}

when HTTP_RESPONSE {
  if { $flag eq 0 }{
      HTTP::header insert "Set-Cookie"  "MyCookie=MyValue;path=/"
  }
  unset flag
}