RSA 公開鍵を C# で JWKs(JSON Web Key Set) に出力する

jose-jwt など C# のライブラリではサポートされていなかったので。

using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using Microsoft.IdentityModel.Tokens;
using Newtonsoft.Json;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.OpenSsl;

namespace TestCommands
{
    class Jwks
    {
        private const string PUBLIC_KEY = @"-----BEGIN PUBLIC KEY-----
MIIBITANBgkqhkiG9w0BAQEFAAOCAQ4AMIIBCQKCAQB5uVaCLL+DmPblCSJas1iC
MqY2XI4yZ3w5mj9gcXG9RqjWiZ8hSv+In1pUl4MSVoykd/Sd3khd6kKLt5GI40Ix
rs1f/DZBYdUYgNhc1pJU3AiOFx/xFmVFACwJM+fVkuJ/hXrHDsWK3AQdCcvrIBjs
RstK5ZzJOHW6doMsawle1EGbhxazBglVwE6zgyMAeGehZHzekj9bliEB4Pxn4Eir
VAPN6bbZ0CYygUQiKCV/L6lMR6IMtqG165rj32bOFdm3H8p/XUA5Rzn1HJe6T8JU
gEJRVIMrYegHclOmxS/LhhJZ7uXuDjex6NlciBlbwWXO6RBDyupwYuY7m8DWqML3
AgMBAAE=
-----END PUBLIC KEY-----";
        static void Main(string[] args)
        {
            using (var textReader = new StringReader(PUBLIC_KEY))
            {
                var pubkeyReader = new PemReader(textReader);
                RsaKeyParameters KeyParameters = (RsaKeyParameters)pubkeyReader.ReadObject();
                var e = Base64UrlEncoder.Encode(KeyParameters.Exponent.ToByteArrayUnsigned());
                var n = Base64UrlEncoder.Encode(KeyParameters.Modulus.ToByteArrayUnsigned());
                var dict = new Dictionary<string, string>() {
                    {"e", e},
                    {"kty", "RSA"},
                    {"n", n}
                };
                var hash = SHA256.Create();
                Byte[] hashBytes = hash.ComputeHash(System.Text.Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(dict)));
                JsonWebKey jsonWebKey = new JsonWebKey()
                {
                    Kid = Base64UrlEncoder.Encode(hashBytes),
                    Kty = "RSA",
                    E = e,
                    N = n
                };
                JsonWebKeySet jsonWebKeySet = new JsonWebKeySet();
                jsonWebKeySet.Keys.Add(jsonWebKey);

                System.Console.WriteLine(JsonConvert.SerializeObject(jsonWebKeySet));
            }
        }
    }
}