Terminate user session

Hello, Is there any way I can terminate a specific user's session server side? Any solution as close to PHP as it gets would be great. Maybee I can immitate somehow the package sent to the access point to notice the session is terminated, or maybee there is a command line or something... At this point in my script I have the user's credentials, the access point's IP and listening port. I hope I can get somewhere from there. Thanks in advance. Benoit