generate_challenge() only generated half as many bytes as it should.
generate_challenge() only generated half as many bytes as it should.

Changed generate_challenge() to generating bytes instead of a hex
encoded string, to not have to decode what we just encoded - instead
just generate plain bytes of randomness and then encode them once.

Yubico/yubico-pam,madrat-/yubico-pam,eworm-de/yubico-pam,Yubico/yubico-pam,eworm-de/yubico-pam,eworm-de/yubico-pam,madrat-/yubico-pam,Yubico/yubico-pam,madrat-/yubico-pam