Do you want the name of the user on the client station or on the server ?

The username of the client station cannot be obtained, unless it is passed to the server as an argument in a request.

The username of the server station will be the one that was used for launching Apache, which is rarely interesting. Anyway, sometimes, there is an environment variable holding it. Open a console window, and type "Set" in order to view all the environment variables. One of them might the one you are looking for.