uses http://sourceforge.net/projects/phpqrcode/ for qr code generation - LGPLv3
uses https://www.cnysupport.com/ga.txt for computation - GPL v3
create QR Code for HOTP Google Authenticator without using google charts API
origin: https://www.cnysupport.com/index.php/free-stuff/using-google-authenticator-with-apache-mod_authn_otp