I assumed you're installing your copy of Xampp in c:\xampp

First, do make sure you have the library file named 'php_openssl.dll' in your c:\xampp\php\ext directory or just paste this script below into command line and run it :

if exist c:\xampp\php\ext\php_openssl.dll (echo YES) else (echo NO)

Next, go open the 'c:\xampp\php\php.ini' file and remove the semicolon to:

;extension=php_openssl.dll

If you don't have that line, just write that line down (without semicolon of course), in the "Dynamic Extensions" section. Don't forget to save it.

 Last, restart the Apache service through XAMPP panel, and you're done :-)