ERP_Auth_Service/Utility/RsaKeyProvider.cs

using System.Security.Cryptography;
using System.Text;
using Microsoft.IdentityModel.Tokens;

namespace AuthHex.Utility;

public class RsaKeyProvider
{
    private readonly RSA _rsa;

    public RsaKeyProvider(string privateKeyXml)
    {
        _rsa = RSA.Create();
        _rsa.FromXmlString(privateKeyXml);
    }

    public RsaSecurityKey GetPrivateKey()
    {
        var key = new RsaSecurityKey(_rsa);
        var publicParameters = _rsa.ExportParameters(false);
        key.KeyId = ComputeKeyId(publicParameters);
        return key;
    }

    public RsaSecurityKey GetPublicKey()
    {
        var publicKeyRsa = RSA.Create();
        var publicParameters = _rsa.ExportParameters(false);
        publicKeyRsa.ImportParameters(publicParameters);

        var key = new RsaSecurityKey(publicKeyRsa);
        key.KeyId = ComputeKeyId(publicParameters);
        return key;
    }

    private static string ComputeKeyId(RSAParameters publicParameters)
    {
        var modulus = publicParameters.Modulus ?? Array.Empty<byte>();
        var exponent = publicParameters.Exponent ?? Array.Empty<byte>();
        var payload = $"{Convert.ToBase64String(modulus)}.{Convert.ToBase64String(exponent)}";

        var hash = SHA256.HashData(Encoding.UTF8.GetBytes(payload));
        return Base64UrlEncoder.Encode(hash);
    }

    public static (string privateKey, string publicKey) GenerateKeys()
    {
        using var rsa = RSA.Create(2048);
        var privateKey = rsa.ToXmlString(true);  // includes private key
        var publicKey = rsa.ToXmlString(false);   // public key only
        return (privateKey, publicKey);
    }
}