基于.net4.0实现IdentityServer4客户端JWT解密

情景：公司项目基于.net4.0,web客户端实现单点登录需要自己解密id_token，对于jwt解密，.net提供了IdentityModel类库，但是4.0中该类库不可用，所以自己实现了解密方法..

使用了类库：链接地址

下面直接贴代码，直接调用DecodeJWT方法就行，参数为id_token，key默认为空字符串"",

代码

public static IDictionary<string, object> DecodeJWT(string jwttoken,string key)    {      //从/.well-known/openid-configuration路径获取jwks_uri      var webClient = new WebClient();      var endpoint = "http://localhost:5000/.well-known/openid-configuration";      var json = webClient.DownloadString(endpoint);      JObject metadata = JsonConvert.DeserializeObject<JObject>(json);      var jwksUri = metadata["jwks_uri"].ToString();      //从jwks_uri获取keys      json = webClient.DownloadString(jwksUri);      var keys = JsonConvert.DeserializeObject<CustomJWKs>(json);      //从jwt获取头部kid,并从keys中找到匹配kid的key      string[] tokenParts = jwttoken.Split('.');      byte[] bytes = FromBase64Url(tokenParts[0]);      string head= Encoding.UTF8.GetString(bytes);      string kid = JsonConvert.DeserializeObject<JObject>(head)["kid"].ToString();      var defaultkey=keys.keys.Where(t => t.kid == kid).FirstOrDefault();      if(defaultkey==null)      {        throw new Exception("未找到匹配的kid");      }      //jwt解密      return RS256Decode(jwttoken, key, defaultkey.e, defaultkey.n);    }     public static IDictionary<string, object> RS256Decode(string token, string secret, string exponent,string modulus)    {      try      {        IJsonSerializer serializer = new JsonNetSerializer();        IDateTimeProvider provider = new UtcDateTimeProvider();        IJwtValidator validator = new JwtValidator(serializer, provider);        IBase64UrlEncoder urlEncoder = new JwtBase64UrlEncoder();        RSAlgorithmFactory rS256Algorithm = new RSAlgorithmFactory(() =>        {          RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();          rsa.ImportParameters(           new RSAParameters()           {             Modulus = FromBase64Url(modulus),             Exponent = FromBase64Url(exponent)           });          byte[] rsaBytes = rsa.ExportCspBlob(true);          X509Certificate2 cert = new X509Certificate2(rsaBytes);          return cert;        });        IJwtDecoder decoder = new JwtDecoder(serializer, validator, urlEncoder, rS256Algorithm);        var json = decoder.DecodeToObject(token, secret, verify: false);        return json;      }      catch (TokenExpiredException)      {        throw new Exception("token已过期");        //Console.WriteLine("Token has expired");        //return null;      }      catch (SignatureVerificationException)      {        throw new Exception("token验证失败");        //Console.WriteLine("Token has invalid signature");        //return null;      }    }    public static byte[] FromBase64Url(string base64Url)    {      string padded = base64Url.Length % 4 == 0        ? base64Url : base64Url + "====".Substring(base64Url.Length % 4);      string base64 = padded.Replace("_", "/")                 .Replace("-", "+");      return Convert.FromBase64String(base64);}