Run PHP Script to Fill Custom Profile Field

Hello,

I have a script that outputs a special key. What I would like to do is have a member able to go to their profile and, one time only, click a button to generate a key. Although, I need it to send their username as a variable to the php script it runs as it generates the key.

If anyone knows at least a way to run a php script that pulls the users username into it that would be great. I could at least make a separate page for it.

Thanks!!