remove dupicate Identity (#18061)

* remove dupicate Identity

* remove dupicate Identity

* remove dupicate Identity

* remove dupicate Identity

* work

Author: Rick-Anderson

aspnetcore/security/authentication/scaffold-identity.md

@@ -5,7 +5,7 @@ description: Learn how to scaffold Identity in an ASP.NET Core project.
 monikerRange: '>= aspnetcore-2.1'
 ms.author: riande
 ms.custom: mvc
-ms.date: 01/15/2020
+ms.date: 5/1/2020
 uid: security/authentication/scaffold-identity
 ---
 # Scaffold Identity in ASP.NET Core projects
@@ -24,7 +24,19 @@ We recommend using a source control system that shows file differences and allow
 
 Services are required when using [Two Factor Authentication](xref:security/authentication/identity-enable-qrcodes), [Account confirmation and password recovery](xref:security/authentication/accconfirm), and other security features with Identity. Services or service stubs aren't generated when scaffolding Identity. Services to enable these features must be added manually. For example, see [Require Email Confirmation](xref:security/authentication/accconfirm#require-email-confirmation).
 
-This document contains more complete instructions than the *ScaffoldingReadme.txt* file which is generated when running the scaffolder.
+When scaffolding Identity with a new data context into a project with existing individual accounts:
+
+* In `Startup.ConfigureServices`, remove the calls to:
+  * `AddDbContext`
+  * `AddDefaultIdentity`
+
+For example, `AddDbContext` and `AddDefaultIdentity` are commented out in the following code:
+
+[!code-csharp[](scaffold-identity/3.1sample/StartupRemove.cs?name=snippet)]
+
+The preceeding code comments out the code that is duplicated in *Areas/Identity/IdentityHostingStartup.cs*
+
+Typically, apps that were created with individual accounts should ***not*** create a new data context.
 
 ## Scaffold identity into an empty project
 

aspnetcore/security/authentication/scaffold-identity/3.1sample/StartupRemove.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Identity;
+using Microsoft.AspNetCore.Identity.UI;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.HttpsPolicy;
+using Microsoft.EntityFrameworkCore;
+using AddDefaultIdentity.Data;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+
+namespace AddDefaultIdentity
+{
+    public class StartupRemove
+    {
+        public StartupRemove(IConfiguration configuration)
+        {
+            Configuration = configuration;
+        }
+
+        public IConfiguration Configuration { get; }
+
+        // This method gets called by the runtime. Use this method to add services to the container.
+        #region snippet
+        public void ConfigureServices(IServiceCollection services)
+        {
+            //services.AddDbContext<ApplicationDbContext>(options =>
+            //    options.UseSqlServer(
+            //        Configuration.GetConnectionString("DefaultConnection")));
+            //services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
+            //    .AddEntityFrameworkStores<ApplicationDbContext>();
+            services.AddControllersWithViews();
+            services.AddRazorPages();
+        }
+        #endregion
+
+        // 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.UseDatabaseErrorPage();
+            }
+            else
+            {
+                app.UseExceptionHandler("/Home/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();
+
+            app.UseRouting();
+
+            app.UseAuthentication();
+            app.UseAuthorization();
+
+            app.UseEndpoints(endpoints =>
+            {
+                endpoints.MapControllerRoute(
+                    name: "default",
+                    pattern: "{controller=Home}/{action=Index}/{id?}");
+                endpoints.MapRazorPages();
+            });
+        }
+    }
+}