title: Where is the IApplicationBuilder UseCookieAuthentication extension method?
body: <p>I downloaded a private git project other developers have been working on for a few months. When building the project, I ran into a few issues:</p>
  
  <ul>
  <li>To restore packages initially, I needed to do <code>dnu restore</code> from the command line. Package restore from within Visual Studio 2015 seems to work fine after that.</li>
  <li>One project still had a few missing references in .cs files. I fixed it by adding packages to the respective <code>project.json</code> file.</li>
  </ul>
  
  <p>Now I am left with only one error:
  <code>IApplicationBuilder does not contain a definition for 'UseCookieAuthentication</code>...</p>
  
  <p>The code expects an anonymous function:</p>
  
  <pre><code>app.UseCookieAuthentication(options =&gt;
  {
      options.AuthenticationScheme = "NLCookieMiddleware";
      options.LoginPath = new PathString("/api/Account/Login/");
      //options.AccessDeniedPath = new PathString("/Account/Forbidden/");
      options.AutomaticAuthenticate = true;
      options.AutomaticChallenge = true;
  });
  </code></pre>
  
  <p>What's confusing to me is that other developers builds are fine without having added any other references to their project.json files. The working file for them is:</p>
  
  <pre><code>{
    "webroot": "wwwroot",
    "version": "1.0.0-*",
    "dependencies": {
      "AutoMapper": "3.3.1",
      "Core": "1.0.0-*",
      "Data.EF": "1.0.0-*",
      "FluentMigrator": "1.6.0",
      "HtmlAgilityPack": "1.4.9",
      "Microsoft.AspNet.Diagnostics": "1.0.0-rc1-final",
      "Microsoft.AspNet.Hosting": "1.0.0-rc1-final",
      "Microsoft.AspNet.Identity": "3.0.0-rc1-final",
      "Microsoft.AspNet.Identity.EntityFramework": "3.0.0-rc1-final",
      "Microsoft.AspNet.Identity.Owin": "1.0.0-rc1",
      "Microsoft.AspNet.Mvc": "6.0.0-rc1-final",
      "Microsoft.AspNet.Mvc.Core": "6.0.0-rc1-final",
      "Microsoft.AspNet.StaticFiles": "1.0.0-rc1-final",
      "Microsoft.AspNet.Server.Kestrel": "1.0.0-rc1-final",
      "Microsoft.AspNet.Server.WebListener": "1.0.0-rc1-final",
      "Microsoft.AspNet.IISPlatformHandler": "1.0.0-rc1-final",
      "Microsoft.Extensions.Configuration.Abstractions": "1.0.0-rc1-final",
      "Microsoft.Extensions.Configuration": "1.0.0-rc1-final",
      "WindowsAzure.Storage": "5.0.0",
      "System.Net.Http": "4.0.0",
      "RazorEngine": "4.2.3-beta1",
      "Microsoft.AspNet.Razor": "4.0.0-rc1-final",
      "premailer.net": "1.4.2",
      "Microsoft.Net.Http.Client": "1.0.0-beta6",
      "Moq": "4.2.1510.2205",
      "Serilog.Framework.Logging": "1.0.0-rc1-final-10071",
      "Microsoft.AspNet.WebApi.Client": "5.2.3",
      "Microsoft.Net.Http.Server": "1.0.0-rc1-final",
      "StructureMap.Dnx": "0.4.0-alpha4"
    },
    "commands": {
      "web": "Microsoft.AspNet.Server.Kestrel"
    },
    "frameworks": {
      "dnx451": {
        "dependencies": {
          "CMS.Services.Contracts": "1.0.0-*",
          "CSharpSDK": "1.0.0-*",
          "Lookups.Contracts": "1.0.0-*",
          "Services.Internal.Contracts": "1.0.0-*"
        },
        "frameworkAssemblies": {
          "System.ServiceModel": "4.0.0.0",
          "System.DirectoryServices.AccountManagement": "4.0.0.0"
        }
      }
    },
    "exclude": [
      "wwwroot",
      "node_modules",
      "bower_components"
    ],
    "publishExclude": [
      "node_modules",
      "bower_components",
      "**.xproj",
      "**.user",
      "**.vspscc"
    ]
  }
  </code></pre>
  
  <p>I've added countless other packages and tried older versions of them with no luck:</p>
  
  <ul>
  <li>Microsoft.AspNet.Authentication.Cookies</li>
  <li>Microsoft.Owin.Security.Cookies.Interop</li>
  </ul>
  
  <p>Where does this extension method live? Why would other developers not have this issue?</p>