EnvelopeGenerator/EnvelopeGenerator.Application/Services/Authenticator.cs

using EnvelopeGenerator.Application.Configurations;
using EnvelopeGenerator.Application.Contracts.Services;
using Microsoft.Extensions.Options;
using OtpNet;
using QRCoder;
using System.Text;

namespace EnvelopeGenerator.Application.Services;

/// <summary>
/// 
/// </summary>
public class Authenticator : IAuthenticator
{
    /// <summary>
    /// 
    /// </summary>
    public static Lazy<Authenticator> LazyStatic => new(() => new Authenticator(Options.Create<AuthenticatorParams>(new()), new QRCodeGenerator()));

    /// <summary>
    /// 
    /// </summary>
    public static Authenticator Static => LazyStatic.Value;

    private readonly AuthenticatorParams _params;

    private readonly QRCodeGenerator _qrCodeGenerator;

    /// <summary>
    /// 
    /// </summary>
    /// <param name="options"></param>
    /// <param name="qrCodeGenerator"></param>
    public Authenticator(IOptions<AuthenticatorParams> options, QRCodeGenerator qrCodeGenerator)
    {
        _params = options.Value;
        _qrCodeGenerator = qrCodeGenerator;
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="length"></param>
    /// <returns></returns>
    /// <exception cref="ArgumentException"></exception>
    public string GenerateCode(int length)
    {
        //TODO: Inject Random as a singleton to support multithreading to improve performance.
        Random random = new();

        if (length <= 0)
            throw new ArgumentException("Password length must be greater than 0.");

        var passwordBuilder = new StringBuilder(length);

        for (int i = 0; i < length; i++)
            passwordBuilder.Append(_params.CharPool[random.Next(_params.CharPool.Length)]);

        return passwordBuilder.ToString();
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="length"></param>
    /// <returns></returns>
    public string GenerateTotpSecretKey(int? length = null)
        => Base32Encoding.ToString(KeyGeneration.GenerateRandomKey(length ?? _params.DefaultTotpSecretKeyLength));

    /// <summary>
    /// 
    /// </summary>
    /// <param name="userEmail"></param>
    /// <param name="secretKey"></param>
    /// <param name="issuer"></param>
    /// <param name="totpUrlFormat"></param>
    /// <param name="pixelsPerModule"></param>
    /// <returns></returns>
    public byte[] GenerateTotpQrCode(string userEmail, string secretKey, string? issuer = null, string? totpUrlFormat = null, int? pixelsPerModule = null)
    {
        var url = string.Format(totpUrlFormat ?? _params.TotpUrlFormat,
            Uri.EscapeDataString(userEmail),
            Uri.EscapeDataString(secretKey),
            Uri.EscapeDataString(issuer ?? _params.TotpIssuer));
        using var qrCodeData = _qrCodeGenerator.CreateQrCode(url, QRCodeGenerator.ECCLevel.Q);
        using var qrCode = new BitmapByteQRCode(qrCodeData);
        return qrCode.GetGraphic(pixelsPerModule ?? _params.TotpQRPixelsPerModule);
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="userEmail"></param>
    /// <param name="length"></param>
    /// <param name="issuer"></param>
    /// <param name="totpUrlFormat"></param>
    /// <param name="pixelsPerModule"></param>
    /// <returns></returns>
    public byte[] GenerateTotpQrCode(string userEmail, int? length = null, string? issuer = null, string? totpUrlFormat = null, int? pixelsPerModule = null)
    {
        return GenerateTotpQrCode(
            userEmail: userEmail,
            secretKey: GenerateTotpSecretKey(length: length),
            issuer: issuer,
            totpUrlFormat: totpUrlFormat,
            pixelsPerModule: pixelsPerModule);
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="secretKey"></param>
    /// <param name="step"></param>
    /// <returns></returns>
    public string GenerateTotp(string secretKey, int step = 30) => new Totp(Base32Encoding.ToBytes(secretKey), step).ComputeTotp();
    
    /// <summary>
    /// 
    /// </summary>
    /// <param name="totpCode"></param>
    /// <param name="secretKey"></param>
    /// <param name="step"></param>
    /// <param name="window"></param>
    /// <returns></returns>
    public bool VerifyTotp(string totpCode, string secretKey, int step = 30, VerificationWindow? window = null)
        => new Totp(Base32Encoding.ToBytes(secretKey), step).VerifyTotp(totpCode, out _, window);
}