using System;

using Microsoft.IdentityModel.Protocols;

using Microsoft.IdentityModel.Protocols.OpenIdConnect;

using Microsoft.IdentityModel.Tokens;

using System.IdentityModel.Tokens.Jwt;

using System.Threading;

using System.Threading.Tasks;

using System.Net.Http;

public class Program

{

    static void Main(string[] args)

        {

            //var accessToken = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ2ZXIiOjEsImp0aSI6IkFULmtvM3NlRFBndlZmWVRTYk5xUk5TVWcwbWVGclZQQ0NabzU3NjJXRG1YYVkiLCJpc3MiOiJodHRwczovL2Rldi0zNzQyMjY0MS5va3RhLmNvbS9vYXV0aDIvZGVmYXVsdCIsImF1ZCI6ImFwaTovL2RlZmF1bHQiLCJpYXQiOjE2MjMwNDgxNzEsImV4cCI6MTYyMzA1MTc3MSwiY2lkIjoiMG9hdmthZDNzanp1aVF2R2M1ZDYiLCJ1aWQiOiIwMHV2ZXVwd2RxUU4wRGZrRjVkNiIsInNjcCI6WyJvcGVuaWQiLCJwcm9maWxlIl0sInN1YiI6ImFhbWJhbGFAcG1hcGludGVybmFsLm5ldCJ9.S4kUfMZVZDXN3DGA4YDopNKtIt-4N6FHUptlkwokohs";

            var accessToken = "eyJraWQiOiJlaEZzV3ZkaW9UdUE3c01zTVYtb21fNlRCWFo2aVdYLWQ0encxZ1BmVWlFIiwiYWxnIjoiUlMyNTYifQ.eyJ2ZXIiOjEsImp0aSI6IkFULmtvM3NlRFBndlZmWVRTYk5xUk5TVWcwbWVGclZQQ0NabzU3NjJXRG1YYVkiLCJpc3MiOiJodHRwczovL2Rldi0zNzQyMjY0MS5va3RhLmNvbS9vYXV0aDIvZGVmYXVsdCIsImF1ZCI6ImFwaTovL2RlZmF1bHQiLCJpYXQiOjE2MjMwNDgxNzEsImV4cCI6MTYyMzA1MTc3MSwiY2lkIjoiMG9hdmthZDNzanp1aVF2R2M1ZDYiLCJ1aWQiOiIwMHV2ZXVwd2RxUU4wRGZrRjVkNiIsInNjcCI6WyJvcGVuaWQiLCJwcm9maWxlIl0sInN1YiI6Impyb3V0QHByb2Nlc3NtYXAuY29tIn0.PubyBJSTgM3LwaWb9Z2JbAYaL1vvCRIFqLNgAGKiC9J9Az5b6XwLaoP5z-tkZbVhCdXRZjuq-KFG1a5BovknYc4R3MQfNa_fprBlsqwSa9f73cReWsGtgiiK5kUu8ok9EwDq3FKTSmJ4BftvLhBO3zsRbSSALp9JkDIUr8fdJylmh0KmU8ejm5TRc3drRIQhfovPvKWv7jNrjUS8pOoAWMK-VPKTdMKY1v8fgcrDghGVNpJQRgo3kBWkhr8nBtWyYD-HovUEu-wPaCyA0CbXsxAR08_xoRbgdr4r-CWxm2nZ0LyP3tD7ZoX0vCzCKMMe7yiWFjJc7OejPubPgjN8aQ";

            var issuer = "https://dev-37422641.okta.com/oauth2/default";

            var configurationManager = new ConfigurationManager<OpenIdConnectConfiguration>(

     issuer + "/.well-known/oauth-authorization-server",

     new OpenIdConnectConfigurationRetriever(),

     new HttpDocumentRetriever());

​

            var validatedToken =  ValidateToken(accessToken, issuer, configurationManager);

            if (validatedToken.Result == null)

            {

                Console.WriteLine("Invalid token");

            }

            else

            {

                // Additional validation...

                Console.WriteLine("Token is valid!");

            }

        }

​

        private static async Task<JwtSecurityToken> ValidateToken(

    string token,

    string issuer,

    IConfigurationManager<OpenIdConnectConfiguration> configurationManager,

    CancellationToken ct = default(CancellationToken))

        {

            if (string.IsNullOrEmpty(token)) throw new ArgumentNullException(nameof(token));

            if (string.IsNullOrEmpty(issuer)) throw new ArgumentNullException(nameof(issuer));

​

            var discoveryDocument = await configurationManager.GetConfigurationAsync(ct);

            var signingKeys = discoveryDocument.SigningKeys;

​

            var validationParameters = new TokenValidationParameters

            {

                RequireExpirationTime = true,

                RequireSignedTokens = true,

                ValidateIssuer = true,

                ValidIssuer = issuer,

                ValidateIssuerSigningKey = true,

                IssuerSigningKeys = signingKeys,

                ValidateLifetime = true,

                // Allow for some drift in server time

                // (a lower value is better; we recommend two minutes or less)

                ClockSkew = TimeSpan.FromMinutes(2),

                // See additional validation for aud below

            };

​

            try

            {

                var principal = new JwtSecurityTokenHandler().ValidateToken(token, validationParameters, out var rawValidatedToken);

​

                return (JwtSecurityToken)rawValidatedToken;

            }

            catch (SecurityTokenValidationException ex)

            {

                // Logging, etc.

                Console.WriteLine(ex);

​

            }

        }

}