Perl module to register and authenticate U2F compatible devices

 Universal 2nd Factor (U2F) is an open authentication standard that strengthens
 and simplifies two-factor authentication using specialized USB or NFC devices
 based on similar security technology found in smart cards.
 .
 Crypt::U2F::Server module implements the server side of U2F authentication
 through Yubico's C library.
 .
 Prefer to use Crypt::U2F::Server::Simple since Crypt::U2F::Server is a very low
 level wrapper around the original C library.