Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc.Authorization;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.IdentityModel.Tokens;
using Swashbuckle.AspNetCore.Swagger;
using Swashbuckle.AspNetCore.SwaggerGen;

namespace ApiDemo
{
    public class Startup
    {
        private const string SECRET_KEY = "needtogetthisfromenvironment";
        private readonly SymmetricSecurityKey _signingKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(SECRET_KEY));

        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            // Adds services required for using options.
            services.AddOptions();

            // Add framework services.
            services.AddMvc(config => {
                var policy = new AuthorizationPolicyBuilder()
                                 .RequireAuthenticatedUser()
                                 .Build();
                config.Filters.Add(new AuthorizeFilter(policy));
            });

            #region This part is for api server not for token server
            // Use policy auth.
            services.AddAuthorization(options => {
                options.AddPolicy("DisneyUser",
                                  policy => policy.RequireClaim("DisneyCharacter", "IAmMickey"));
            });
            #endregion

            // Get the options from app settings
            var jwtAppSettingOptions = Configuration.GetSection(nameof(JwtIssuerOptions));

            // Configure JwtIssuerOptions
            services.Configure<JwtIssuerOptions>(options => {
                options.Issuer = jwtAppSettingOptions[nameof(JwtIssuerOptions.Issuer)];
                options.Audience = jwtAppSettingOptions[nameof(JwtIssuerOptions.Audience)];
                options.SigningCredentials = new SigningCredentials(_signingKey, SecurityAlgorithms.HmacSha256);
            });

            services.AddSwaggerGen(c =>
            {
                c.SwaggerDoc("v1", new Info { Title = "My API", Version = "v1" });
            });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            #region This part is for api server not for token server
            var jwtAppSettingOptions = Configuration.GetSection(nameof(JwtIssuerOptions));
            var tokenValidationParameters = new TokenValidationParameters
            {
                ValidateIssuer = true,
                ValidIssuer = jwtAppSettingOptions[nameof(JwtIssuerOptions.Issuer)],

                ValidateAudience = true,
                ValidAudience = jwtAppSettingOptions[nameof(JwtIssuerOptions.Audience)],

                ValidateIssuerSigningKey = true,
                IssuerSigningKey = _signingKey,

                RequireExpirationTime = true,
                ValidateLifetime = true,

                ClockSkew = TimeSpan.Zero                
            };

            app.UseJwtBearerAuthentication(new JwtBearerOptions
            {
                AutomaticAuthenticate = true,
                AutomaticChallenge = true,
                TokenValidationParameters = tokenValidationParameters
            });
            #endregion

            app.UseMvc();
            app.UseSwagger();
            app.UseSwaggerUI(c =>
            {
                c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
            });
        }
    }
}