The OnExecute event handler is invoked after the client has
successfully executed an external CGI program or script.
To implement an event handler, the application should create a class
derived from the CHttpServer class, and then override this method.
External programs must be registered by the server application
using the RegisterProgram method. To enable the use of scripts,
the RegisterHandler method can be used to associate an
executable program with a specific file extension.
The GetProgramOutput method can be used to obtain the
unfiltered output from the external command, while the GetProgramText
method will return filtered output from the program that contains only
printable text characters.