README.md

You can generate Totp code based on time, UserSecurityStamp and UserIdentifier and ExpirationTime.

You can use this package instead of Rfc6238AuthenticationService class for generating totp code with identity.

NuGet:

<PackageReference Include="TotpGenerator" Version="1.0.1" />

Usage:

public async ValueTask<int> GetTwoFactorTotpCode(string email)
{
    var user = await GetUserByEmail(email);

    var modifier = GetModifier(user, TotpEnum.TwoFactor);

    var totpCode = TotpService.GenerateCode(user.SecurityStamp.ToString(), modifier);

    return totpCode;
}

public async ValueTask<bool> ValidateTwoFactorTotpCode(string email, int totpCode)
{
    var user = await GetUserByEmail(email);

    string modifier = GetModifier(user, TotpEnum.TwoFactor);

    var isValid = TotpService.ValidateCode(
        user.SecurityStamp.ToString(), 
        totpCode, 
        modifier, 
        _userOption.TwoFactorTotpExpiration);

    return isValid;
}

private static string GetModifier(User user, TotpEnum totpEnum)
{
    return $"Totp:{user.Id}:{totpEnum}";
}

TotpEnum:

public enum TotpEnum : byte
{
    TwoFactor = 1,
    Activation = 2,
    Deactivation = 4
}