Generating and validating One-time Password based on Hash-based Message Authentication Code (HOTP) and Time Based One-time Password (TOTP) according to RFC 4226 <https://tools.ietf.org/html/rfc4226> and RFC 6238 <https://tools.ietf.org/html/rfc6238>.
Maintainer: Randy Lai randy.cs.lai@gmail.com [copyright holder]
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