EnvelopeGenerator/EnvelopeGenerator.Extensions/StringExtension.cs

using OtpNet;

namespace EnvelopeGenerator.Extensions
{
    public static class StringExtension
    {
        public static bool IsValidTotp(string totp, string secret)
        {
            var secret_bytes = Base32Encoding.ToBytes(secret);
            var secret_totp = new Totp(secret_bytes);
            return secret_totp.VerifyTotp(totp, out _, VerificationWindow.RfcSpecifiedNetworkDelay);
        }
    }
}