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

        public static Authenticator Static => LazyStatic.Value;

        private readonly AuthenticatorParams _params;

        private readonly QRCodeGenerator _qrCodeGenerator;

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

        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();
        }

        public string GenerateTotpSecretKey(int? length = null)
            => Base32Encoding.ToString(KeyGeneration.GenerateRandomKey(length ?? _params.DefaultTotpSecretKeyLength));

        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);
        }

        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);
        }

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