php and java applets

Dear all knowing list, I am trying to control the movement of a camera in real time from the web. But I also need to make sure that only the user I specify can have control. What I though I could do was this: launch a java applet from a php page parsing the session id. Then when the user adjusts the controls on the applet, a php page is loaded by the applet, sets the user session with the session id, then sends the control details back to the server and on to the camera. I've given this a go with no luck. When I try to set the session id on the php script that the Java applet loads I get a permissions error (the perms on /tmp are fine). I'm not 100% sure I understand sessions, is my method utterly implausible? Does anyone have any better suggestions? Thanks, Tom Playford