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);}

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