Validating an ADFS JWT token

Helper.cs

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ValidateJWTConsoleApp
{
    class Helper
    {
        internal static class AsyncHelper
        {
            private static readonly TaskFactory TaskFactory = new TaskFactory(CancellationToken.None, TaskCreationOptions.None, TaskContinuationOptions.None, TaskScheduler.Default);

            public static void RunSync(Func<Task> func)
            {
                TaskFactory.StartNew(func).Unwrap().GetAwaiter().GetResult();
            }

            public static TResult RunSync<TResult>(Func<Task<TResult>> func)
            {
                return TaskFactory.StartNew(func).Unwrap().GetAwaiter().GetResult();
            }
        }
    }
}

Program.cs

using System;

using System.IdentityModel.Tokens.Jwt;
using System.Threading;
using Microsoft.IdentityModel.Protocols;
using Microsoft.IdentityModel.Protocols.OpenIdConnect;
using Microsoft.IdentityModel.Tokens;
using static ValidateJWTConsoleApp.Helper;

// Derived from https://www.jerriepelser.com/blog/manually-validating-rs256-jwt-dotnet/

namespace ValidateJWTConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            // ADFS FQDN
            const string ADFSDomain = "https://my-adfs/adfs/";
            // Identifier
            const string ADFSAudience = "https://localhost:44326/"; 
            
            const string testToken = "eyJ...6-1A";

            try
            {
                // Download the OIDC configuration which contains the JWKS
                // NB!!: Downloading this takes time, so do not do it very time you need to validate a token, Try and do it only once in the lifetime of your application!!

                IConfigurationManager<OpenIdConnectConfiguration> configurationManager = new ConfigurationManager<OpenIdConnectConfiguration>($"{ADFSDomain}.well-known/openid-configuration", 
                    new OpenIdConnectConfigurationRetriever());
                OpenIdConnectConfiguration openIdConfig = AsyncHelper.RunSync(async () => await configurationManager.GetConfigurationAsync(CancellationToken.None));

                // Configure the TokenValidationParameters. Assign the SigningKeys which were downloaded from ADFS. 
                // Also set the Issuer and Audience(s) to validate.
                // Note: You need to set the ADFS domain as above so that the program can find the /adfs/.well-known/openid-configuration endpoint.
                //       However, this is not the issuer in the token so you need to add the /adfs/services/trust endpoint as below.
                //       If this is not configured corrrectly, you get the exception:

                //       Message=IDX10205: Issuer validation failed. Issuer: 'http://my-adfs/adfs/services/trust'. 
                //       Did not match: validationParameters.ValidIssuer: 'https://my-adfs/adfs/' or validationParameters.ValidIssuers: 'null'.

                TokenValidationParameters validationParameters =
                    new TokenValidationParameters
                    {
                        ValidIssuer = ADFSDomain,
                        ValidIssuers = new[] { ADFSDomain, "http://my-adfs/adfs/services/trust" },
                        ValidAudiences = new[] { ADFSAudience },
                        IssuerSigningKeys = openIdConfig.SigningKeys
                    };

                // Now validate the token. If the token is not valid for any reason, an exception will be thrown by the method

                SecurityToken validatedToken;
                JwtSecurityTokenHandler handler = new JwtSecurityTokenHandler();
                var user = handler.ValidateToken(testToken, validationParameters, out validatedToken);

                // The ValidateToken method above will return a ClaimsPrincipal. Get the claims form user.Claims.
                // These are OAuth claims e.g. "aud", "iss" etc.
                
                Console.WriteLine("Token is validated" + "\n");

                foreach (var Claim in user.Claims)
                {
                    Console.WriteLine("Claim is " + Claim);
                }
            }

            catch (Exception e)
            {
                Console.WriteLine($"Error occurred while validating token: {e.Message}");
            }

            Console.WriteLine();
            Console.WriteLine("Press ENTER to continue...");
            Console.ReadLine();
        }
    }
}

https://medium.com/the-new-control-plane/validating-an-adfs-jwt-token-1146bb529a2a