Startup.cs

using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.EntityFrameworkCore;
using WebApi.Helpers;
using WebApi.Services;
using AutoMapper;
using Microsoft.IdentityModel.Tokens;
using System.Text;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.Extensions.Options;
using System;
using WebApi.Entities;
using Microsoft.AspNetCore.Identity;
using WebApi.Models;

namespace WebApi
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors();
            services.AddDbContext<DataContext>(x => x.UseInMemoryDatabase("TestDb"));
            services.AddMvc();
            services.AddAutoMapper();
            services.AddIdentity<ApplicationUser, ApplicationRole>().AddEntityFrameworkStores<DataContext>().AddDefaultTokenProviders();

            // configure strongly typed settings objects
            var appSettingsSection = Configuration.GetSection("AppSettings");
            services.Configure<AppSettings>(appSettingsSection);

            // configure jwt authentication
            var appSettings = appSettingsSection.Get<AppSettings>();

            var jwtAppSettingOptions = Configuration.GetSection(nameof(JwtIssuerOptions));
            var key = Encoding.ASCII.GetBytes(appSettings.Secret);

            var tokenValidationParameters = new TokenValidationParameters
            {
                ValidateIssuerSigningKey = true,
                IssuerSigningKey = new SymmetricSecurityKey(key),
                ValidateIssuer = false,
                ValidateAudience = false
            };

            services.AddAuthentication(x =>
            {
                x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            })
            .AddJwtBearer(configureOptions =>
            {
                configureOptions.ClaimsIssuer = jwtAppSettingOptions[nameof(JwtIssuerOptions.Issuer)];
                configureOptions.TokenValidationParameters = tokenValidationParameters;
                configureOptions.SaveToken = true;
            }); 

            // configure DI for application services
            services.AddScoped<IUserService, UserService>();
        }

        // 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, IServiceProvider serviceProvider)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            // global cors policy
            app.UseCors(x => x
                .AllowAnyOrigin()
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials());

            app.UseAuthentication();

            app.UseMvc();

            CreateRoles(serviceProvider).Wait();
        }

        private async Task CreateRoles(IServiceProvider serviceProvider)
        {
            //adding custom roles
            var RoleManager = serviceProvider.GetRequiredService<RoleManager<ApplicationRole>>();
            var UserManager = serviceProvider.GetRequiredService<UserManager<ApplicationUser>>();
            string[] roleNames = { "Admin", "Manager", "Member" };
            IdentityResult roleResult;
            foreach (var roleName in roleNames)
            {
                //creating the roles and seeding them to the database
                var roleExist = await RoleManager.RoleExistsAsync(roleName);
                if (!roleExist)
                {
                    roleResult = await RoleManager.CreateAsync(new ApplicationRole(roleName));
                }
            }
            //creating a super user who could maintain the web app
            var poweruser = new ApplicationUser()
            {
                UserName = Configuration.GetSection("UserSettings")["UserName"],
                FullName = Configuration.GetSection("UserSettings")["FullName"],
                PhoneNumber = Configuration.GetSection("UserSettings")["PhoneNumber"],
                Photo = Configuration.GetSection("UserSettings")["Photo"],
                Status = "Active",
                Registered = DateTime.Now                
            };

            string UserPassword = Configuration.GetSection("UserSettings")["UserPassword"];
            var _user = await UserManager.FindByNameAsync(Configuration.GetSection("UserSettings")["UserName"]);
            if (_user == null)
            {
                var createPowerUser = await UserManager.CreateAsync(poweruser, UserPassword);
                if (createPowerUser.Succeeded)
                {
                    //here we tie the new user to the "Admin" role 
                    await UserManager.AddToRoleAsync(poweruser, "Admin");
                }
            }
        }

    }
}