sim756.TOTP

RFC 6238 (TOTP) - Time-Based One-Time Password Generator.

https://www.nuget.org/packages/sim756.TOTP

https://github.com/sim756/sim756.TOTP

string totp = new TOTPGenerator().Compute("QWERTYUIOPASDFGH");

string nextTotp = new TOTPGenerator().Compute("QWERTYUIOPASDFGH", DateTime.UtcNow.AddSeconds(30));

string hotp = new TOTPGenerator()
{
  KeyString = "QWERTYUIOPASDFGH",
  Length = 6,
  Steps = 30
}.Compute();

For HOTP, please check this library:

NuGet - sim756.HOTP - https://www.nuget.org/packages/sim756.HOTP
GitHub - sim756.HOTP - https://www.github.com/sim756/sim756.HOTP