Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.EntityFrameworkCore.SqlServer;
using Microsoft.AspNetCore.Identity.UI;
using Microsoft.Extensions.Hosting;
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Cors;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;
using OnlineLearningSystem.Models;
using OnlineLearningSystem.Services;
using Microsoft.AspNetCore.Mvc.NewtonsoftJson;
using System.Text;

namespace OnlineLearningSystem
{
    public class Startup
    {
        readonly string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";
        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)
        {
            //Inject Appsettings
            services.Configure<ApplicationSettings>(Configuration.GetSection("ApplicationSettings"));

            services.AddCors(options =>
            {
                options.AddPolicy(name: MyAllowSpecificOrigins,
                                  builder =>
                                  {
                                      builder.WithOrigins("http://localhost:4200") //remove the last slash
                                      .AllowAnyHeader()
                                      .AllowAnyMethod();
                                  });
            });
            services.AddControllers();
            services.AddControllersWithViews()
            .AddNewtonsoftJson(options =>
            options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
            );
            services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("IdentityConnection")));  
            
            //Add Repositories Services here
            services.AddScoped<ICourseRepository, CourseRepository>();
            services.AddScoped<ICategoryRepository, CategoryRepository>();
            services.AddScoped<ISectionRepository, SectionRepository>();
            services.AddScoped<IVideoRepository, VideoRepository>();
            services.AddScoped<IEnrollmentRepository, EnrollmentRepository>();

            services.AddIdentity<ApplicationUser, IdentityRole>()
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultTokenProviders().AddRoles<IdentityRole>();

            //Here we can customize the default settings for validation
            //Removing UserName might be done from here
            services.Configure<IdentityOptions>(options =>
            {
                options.Password.RequireDigit = false;
                options.Password.RequireNonAlphanumeric = false;
                options.Password.RequireLowercase = false;
                options.Password.RequireUppercase = false;
                options.Password.RequiredLength = 5;

            });

            //Jwt Authentication

            var key = Encoding.UTF8.GetBytes(Configuration["ApplicationSettings:JWT_Secret"].ToString());

            services.AddAuthentication(x =>
            {
                x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
                x.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
            }).AddJwtBearer(x => {
                x.RequireHttpsMetadata = false;
                x.SaveToken = false;
                x.TokenValidationParameters = new Microsoft.IdentityModel.Tokens.TokenValidationParameters
                {
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = new SymmetricSecurityKey(key),
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    ClockSkew = TimeSpan.Zero
                };
            });

            services.AddMvc();

        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();

            app.UseCors(MyAllowSpecificOrigins);

            // app.UseResponseCaching();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }
}