I have a application (made in Delphi) that contains a Authentication system (login & password).

This system is in PHP, and the application get results from PHP using HTTP GET method. The system returns 'OK' if login and password are correct, and 'NO' if not correct.

Like this...

procedure Check;
var
 x: string;
begin
 x:=Get('www.mywebsite.com/auth.php?user=xxxxxx&pass=zzzzzz');
 if x='OK' then 
  UnlockFeatures
 else
  MessageBox(0,'You're not VIP','Error',0);
end;

Well, it works fine, but it is very easy to circumvent this system with sniffers, packet editor or proxy.

So, I want to get some information (in PHP) that changes every time, and that could be possible get the same information by my application.

What can I do?

I don't need codes. Just tips, suggestions, please...

Thanks...