Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Host.Data;
using Host.Configuration;
using IdentityServer4.Models;
using Microsoft.Extensions.Hosting;
using FluentValidation.AspNetCore;
using Host.Services;
using Host.Models.Validator;

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

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
           
            services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

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

            services.AddControllersWithViews()
                .AddFluentValidation(e => e.RegisterValidatorsFromAssemblyContaining<LoginViewModelValidator>());

            services.AddIdentityServer()
                .AddDeveloperSigningCredential()
                .AddInMemoryIdentityResources(Host.Configuration.Resources.GetIdentityResources())
                .AddInMemoryApiResources(Host.Configuration.Resources.GetApiResources())
                .AddInMemoryClients(Clients.Get())
                .AddAspNetIdentity<ApplicationUser>();

            services.AddScoped<ILabelService, LabelService>();
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                //app.UseDatabaseErrorPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }

            app.UseStaticFiles();

            app.UseRouting();

            app.UseIdentityServer();

            app.UseAuthorization();

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