Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.SpaServices.AngularCli;
using Microsoft.EntityFrameworkCore;
using IdentityAuth.Data;
using IdentityAuth.Models;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.IdentityModel.Tokens;
using System.Text;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.OpenApi.Models;
using System;

namespace IdentityAuth
{
    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.AddSwaggerGen(setup =>
        {
            // Include 'SecurityScheme' to use JWT Authentication
            var jwtSecurityScheme = new OpenApiSecurityScheme
            {
                Scheme = "bearer",
                BearerFormat = "JWT",
                Name = "JWT Authentication",
                In = ParameterLocation.Header,
                Type = SecuritySchemeType.Http,
                Description = "Put **_ONLY_** your JWT Bearer token on textbox below!",

                Reference = new OpenApiReference
                {
                    Id = JwtBearerDefaults.AuthenticationScheme,
                    Type = ReferenceType.SecurityScheme
                }
            };

            setup.AddSecurityDefinition(jwtSecurityScheme.Reference.Id, jwtSecurityScheme);

            setup.AddSecurityRequirement(new OpenApiSecurityRequirement
            {
                { jwtSecurityScheme, Array.Empty<string>() }
            });

        });

            services.AddCors(options =>
                {
                    options.AddPolicy("CorsPolicy",
                        builder => builder.AllowAnyOrigin()
                            .AllowAnyMethod()
                            .AllowAnyHeader());
                });

            services.AddDbContext<ApplicationDbContext>(p => p.UseNpgsql(Configuration.GetConnectionString("DefaultConnection")));

            services.AddDefaultIdentity<ApplicationUser>(options => options.SignIn.RequireConfirmedAccount = true)
                .AddEntityFrameworkStores<ApplicationDbContext>();

            services.AddIdentityServer()
                .AddApiAuthorization<ApplicationUser, ApplicationDbContext>();

            services.AddAuthentication(x =>
            {
                x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            })
            .AddJwtBearer(x =>
            {
                x.RequireHttpsMetadata = false;
                x.SaveToken = true;
                x.TokenValidationParameters = new TokenValidationParameters
                {
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(Configuration.GetSection("AppSettings:Token").Value)),
                    ValidateIssuer = false,
                    ValidateAudience = false
                };
            });
            
            services.AddControllersWithViews();
            services.AddRazorPages();
            // In production, the Angular files will be served from this directory
            services.AddSpaStaticFiles(configuration =>
            {
                configuration.RootPath = "ClientApp/dist";
            });

           
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            //added
            app.UseSwagger();
            app.UseSwaggerUI(x => x.SwaggerEndpoint("/swagger/v1/swagger.json", "ASP.NET Core Identity Auth"));



            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseDatabaseErrorPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            if (!env.IsDevelopment())
            {
                app.UseSpaStaticFiles();
            }

            app.UseRouting();

            // global cors policy
            app.UseCors("CorsPolicy");

            app.UseAuthentication();
            // app.UseIdentityServer();
            app.UseAuthorization();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller}/{action=Index}/{id?}");
                endpoints.MapRazorPages();
            });

            app.UseSpa(spa =>
            {
                // To learn more about options for serving an Angular SPA from ASP.NET Core,
                // see https://go.microsoft.com/fwlink/?linkid=864501

                spa.Options.SourcePath = "ClientApp";

                if (env.IsDevelopment())
                {
                    spa.UseAngularCliServer(npmScript: "start");
                }
            });


        }
    }
}