title: IApplicationBuilder does not contain a definition for UseIdentity
body: <p>I'm following an example to configure AspNet Core Identity on <strong>AspNet Core 3.0</strong></p>
  
  <p>Here's the code for StartUp.cs file</p>
  
  <pre><code>using Microsoft.AspNetCore.Builder;
  using Microsoft.AspNetCore.Hosting;
  using Microsoft.AspNetCore.Identity;
  using Microsoft.EntityFrameworkCore;
  using Microsoft.Extensions.Configuration;
  using Microsoft.Extensions.DependencyInjection;
  using Users_WEB_APP.Models;
  
  namespace Users_WEB_APP
  {
      public class Startup
      {
          public IConfiguration Configuration { get; }
          public Startup(IConfiguration configuration)
          {
              Configuration = configuration;
          }
  
          // This method gets called by the runtime. Use this method to add services to the container.
          public void ConfigureServices(IServiceCollection services)
          {
              services.AddDbContext&lt;AppIdentityDbContext&gt;(options =&gt; options.UseSqlServer(Configuration["Data:ASPNET_IDENTITY:ConnectionString"]));
              services.AddIdentity&lt;AppUser, IdentityRole&gt;()
                  .AddEntityFrameworkStores&lt;AppIdentityDbContext&gt;();
              services.AddMvc(options =&gt; options.EnableEndpointRouting = false);
          }
  
          // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
          public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
          {
              app.UseStatusCodePages();
              app.UseDeveloperExceptionPage();
              app.UseStaticFiles();
              app.UseIdentity();
              app.UseMvcWithDefaultRoute();
          }
      }
  }
  </code></pre>
  
  <p>But at line
  <strong>app.UseIdentity();</strong>
  I'm getting the error</p>
  
  <blockquote>
    <p>'IApplicationBuilder' does not contain a definition for 'UseIdentity',
    and no accessible extension method 'UseIdentity' accepting a first
    argument of type 'IApplicationBuilder' could be found (are you messing
    a using directive or an assembly reference?)</p>
  </blockquote>
  
  <p><strong>What is it that I'm doing Wrong?</strong></p>