Implement JWT decryption on IdentityServer4 client based on .net4.0

scene:The company's project is based on .net4.0. The web client needs to decrypt id_token by itself. For jwt decryption, .net provides an IdentityModel class library, but this class library is not available in 4.0, so I implement the decryption method by myself..

Class library is used:Link address

The following is the code, and the DecodeJWT method can be called directly. The parameter is id_token, and the key defaults to an empty string "",

Code

public static IDictionary&lt;string, object&gt; DecodeJWT(string jwttoken,string key)
    {

      //Get jwks_uri from /.well-known/openid-configuration path      var webClient = new WebClient();

      var endpoint = "http://localhost:5000/.well-known/openid-configuration";

      var json = (endpoint);

      JObject metadata = &lt;JObject&gt;(json);

      var jwksUri = metadata["jwks_uri"].ToString();

      //Get keys from jwks_uri      json = (jwksUri);

      var keys = &lt;CustomJWKs&gt;(json);


      //Get the head kid from jwt and find the key matching kid from keys      string[] tokenParts = ('.');
      byte[] bytes = FromBase64Url(tokenParts[0]);
      string head= Encoding.(bytes);
      string kid = &lt;JObject&gt;(head)["kid"].ToString();

      var defaultkey=(t =&gt;  == kid).FirstOrDefault();

      if(defaultkey==null)
      {
        throw new Exception("No matching kid found");
      }

      //jwt decryption      return RS256Decode(jwttoken, key, , );
    }


     public static IDictionary&lt;string, object&gt; 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(() =&gt;
        {
          RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
          (
           new RSAParameters()
           {
             Modulus = FromBase64Url(modulus),
             Exponent = FromBase64Url(exponent)
           });


          byte[] rsaBytes = (true);

          X509Certificate2 cert = new X509Certificate2(rsaBytes);
          return cert;
        });

        IJwtDecoder decoder = new JwtDecoder(serializer, validator, urlEncoder, rS256Algorithm);
        var json = (token, secret, verify: false);
        return json;
      }
      catch (TokenExpiredException)
      {
        throw new Exception("Token has expired");
        //("Token has expired");
        //return null;
      }
      catch (SignatureVerificationException)
      {
        throw new Exception("Token verification failed");
        //("Token has invalid signature");
        //return null;
      }
    }


    public static byte[] FromBase64Url(string base64Url)
    {
      string padded =  % 4 == 0
        ? base64Url : base64Url + "====".Substring( % 4);
      string base64 = ("_", "/")
                 .Replace("-", "+");
      return Convert.FromBase64String(base64);
}

The above is all the content of this article. I hope it will be helpful to everyone's study and I hope everyone will support me more.