注：本文是【ASP.NET Identity系列教程】的第一篇。本系列教程详细、完整、深入地介绍了微软的ASP.NET Identity技术，描述了如何运用ASP.NET Identity实现应用程序的用户管理，以及实现应用程序的认证与授权等相关技术，译者希望本系列教程能成为掌握ASP.NET Identity技术的一份完整而有价值的资料。读者若是能够按照文章的描述，一边阅读、一边实践、一边理解，定能有意想不到的巨大收获！希望本系列博文能够得到广大园友的高度推荐。

Identity is a new API from Microsoft to manage users in ASP.NET applications. The mainstay for user management in recent years has been ASP.NET Membership, which has suffered from design choices that were reasonable when it was introduced in 2005 but that have aged badly. The biggest limitation is that the schema used to store the data worked only with SQL Server and was difficult to extend without re-implementing a lot of provider classes. The schema itself was overly complex, which made it harder to implement changes than it should have been.
Identity是微软在ASP.NET应用程序中管理用户的一个新的API。近年来用户管理的基石一直是ASP.NET的Membership。Membership在2005年推出时还算是一个合理的选择，但目前看来已经严重过时了。它最大的限制是用以存储数据的架构（Database Schema）只能使用SQL Server，而且难以扩展，除非重新实现大量的提供器类。其数据架构本身也过于复杂，使之比理论上还要难以实现修改。

Microsoft made a couple of attempts to improve Membership prior to releasing Identity. The first was known as simple membership, which reduced the complexity of the schema and made it easier to customize user data but still needed a relational storage model. The second attempt was the ASP.NET universal providers, which I used in Chapter 10 when I set up SQL Server storage for session data. The advantage of the universal providers is that they use the Entity Framework Code First feature to automatically create the database schema, which made it possible to create databases where access to schema management tools wasn't possible, such as the Azure cloud service. But even with the improvements, the fundamental issues of depending on relational data and difficult customizations remained.
在发布Identity之前，微软曾做过两次改善Membership的尝试。第一个尝试称为Simple Membership（简单成员），它降低了数据库架构的复杂性，并使之易于定制用户数据，但仍然需要关系型存储模型。第二个尝试是ASP.NET的Universal Providers（通用提供器），第10章在为会话数据建立SQL Server存储库时曾用过它。Universal Providers的好处是，这些提供器使用了Entity Framework的Code First特性，能够自动地创建数据库架构，使之能够在架构管理工具无法访问的情况下，例如Azure云服务，也能够创建数据库。但即使有了改善，其依赖于关系型数据以及难以定制等根本问题仍然存在。

To address both problems and to provide a more modern user management platform, Microsoft has replaced Membership with Identity. As you'll learn in this chapter and Chapters 14 and 15, ASP.NET Identity is flexible and extensible, but it is immature, and features that you might take for granted in a more mature system can require a surprising amount of work.
为了解决这两个问题并提供一个更现代的用户管理平台，微软用Identity取代了Membership。正如将在本章以及第14、15章所了解到的，ASP.NET Identity灵活且可扩展，但它仍不成熟，你在一些更成熟的系统中能够获得的特性，可能需要超常的工作量。

Microsoft has over-compensated for the inflexibility of Membership and made Identity so open and so adaptable that it can be used in just about any way—just as long as you have the time and energy to implement what you require.
微软已经完全弥补了Membership的不灵活性，使Identity十分开放和广泛适应，几乎能够以任何方式进行使用——只要你有时间有能力做出你所需要的实现即可。

In this chapter, I demonstrate the process of setting up ASP.NET Identity and creating a simple user administration tool that manages individual user accounts that are stored in a database.
在本章中，我会演示建立ASP.NET Identity的过程，并创建一个简单的用户管理工具，用以管理存储在数据库中的个别用户账号。

ASP.NET Identity supports other kinds of user accounts, such as those stored using Active Directory, but I don't describe them since they are not used that often outside corporations (where Active Directive implementations tend to be so convoluted that it would be difficult for me to provide useful general examples).
ASP.NET Identity还支持其他类型的用户账号，例如用Active Directory（活动目录）存储的账号，但我不会对其进行描述，因为这种账号通常不会用于公司的外部（这种场合的Active Directory实现往往很复杂，我难以提供有用的通用示例）。

In Chapter 14, I show you how to perform authentication and authorization using those user accounts, and in Chapter 15, I show you how to move beyond the basics and apply some advanced techniques. Table 13-1 summarizes this chapter.
在第14章中，我将演示如何用这些用户账号进行认证与授权，第15章将演示如何进入高级论题，运用一些高级技术。表13-1是本章概要。

13.1 Preparing the Example Project
13.1 准备示例项目

I created a project called Users for this chapter, following the same steps I have used throughout this book. I selected the Empty template and checked the option to add the folders and references required for an MVC application. I will be using Bootstrap to style the views in this chapter, so enter the following command into the Visual Studio Package Manager Console and press Enter to download and install the NuGet package:
本章根据本书一直采用的同样步骤创建了一个名称为Users的项目。在创建过程中选择了“Empty（空）” 模板，并在“Add the folders and references（添加文件夹和引用）”中选中了“MVC”复选框。本章将使用Bootstrap来设置视图的样式，因此在Visual Studio的“Package Manager Console（包管理器控制台）”中输入以下命令，并按回车，下载并安装这个NuGet包。

Install-Package -version 3.0.3 bootstrap

I created a Home controller to act as the focal point for the examples in this chapter. The definition of the controller is shown in Listing 13-1. I'll be using this controller to describe details of user accounts and data, and the Index action method passes a dictionary of values to the default view via the View method.
我创建了Home控制器，以作为本章示例的焦点。该控制器的定义如清单13-1所示。此控制器将用来描述用户账号的细节和数据，Index动作方法通过View方法给默认视图传递了一个字典值。

using System.Web.Mvc;
using System.Collections.Generic;

namespace Users.Controllers {

    public class HomeController : Controller {

        public ActionResult Index() {
            Dictionary<string, object> data
                = new Dictionary<string, object>();
            data.Add("Placeholder", "Placeholder");
            return View(data);
        }
    }
}

I created a view by right-clicking the Index action method and selecting Add View from the pop-up menu. I set View Name to Index and set Template to Empty (without model). Unlike the examples in previous chapters, I want to use a common layout for this chapter, so I checked the Use a Layout Page option. When I clicked the Add button, Visual Studio created the Views/Shared/_Layout.cshtml and Views/Home/Index.cshtml files. Listing 13-2 shows the contents of the _Layout.cshtml file.
通过右击Index动作方法，并从弹出菜单选择“Add View（添加视图）”，我创建了一个视图。将“View Name（视图名称）”设置为“Index”，并将“Template（模板）”设置为“空（无模型）”。与前面几章的示例不同，本章希望使用一个通用的布局，于是选中了“Use a Layout Page（使用布局页面）”复选框。点击“Add（添加）”按钮后，Visual Studio创建了Views/Shared/_Layout.cshtml和Views/Home/Index.cshtml文件。清单13-2显示了_Layout.cshtml文件的内容。

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>@ViewBag.Title</title>
    <link href="~/Content/bootstrap.min.css" rel="stylesheet" />
    <link href="~/Content/bootstrap-theme.min.css" rel="stylesheet" />
    <style>
        .container { padding-top: 10px; }
        .validation-summary-errors { color: #f00; }
    </style>
</head>
<body class="container">
    <div class="container">
        @RenderBody()
    </div>
</body>
</html>

Listing 13-3 shows the contents of the Index.cshtml file.
清单13-3显示了Index.cshtml文件的内容。

@{
    ViewBag.Title = "Index";
}

<div class="panel panel-primary">
    <div class="panel-heading">User Details</div>
    <table class="table table-striped">
        @foreach (string key in Model.Keys) {
            <tr>
                <th>@key</th>
                <td>@Model[key]</td>
            </tr>
        }
    </table>
</div>

To test that the example application is working, select Start Debugging from the Visual Studio Debug menu and navigate to the /Home/Index URL. You should see the result illustrated by Figure 13-1.
为了测试该应用程序示例能够工作，从Visual Studio的“Debug（调试）”菜单中选择“Start Debugging（启动调试）”，并导航到/Home/Index网址，便可以看到如图13-1所示的结果。

13.2 Setting Up ASP.NET Identity
13.2 建立ASP.NET Identity

For most ASP.NET developers, Identity will be the first exposure to the Open Web Interface for .NET (OWIN). OWIN is an abstraction layer that isolates a web application from the environment that hosts it. The idea is that the abstraction will allow for greater innovation in the ASP.NET technology stack, more flexibility in the environments that can host ASP.NET applications, and a lighter-weight server infrastructure.
对于大多数ASP.NET开发者而言，Identity将是第一个暴露给OWIN（Open Web Interface for .NET——.NET开放Web接口）的组件。OWIN是一个将Web应用程序从托管它的环境中独立出来的抽象层。其思想是这个独立出来的抽象层能够使ASP.NET技术堆栈有更大的创新，使托管ASP.NET应用程序的环境有更多的灵活性，并可以是轻量级的服务器架构。

OWIN is an open standard (which you can read at http://owin.org/spec/owin-1.0.0.html). Microsoft has created Project Katana, its implementation of the OWIN standard and a set of components that provide the functionality that web applications require. The attraction to Microsoft is that OWIN/Katana isolates the ASP.NET technology stack from the rest of the .NET Framework, which allows a greater rate of change.
OWIN是一个开放标准（参阅http://owin.org/spec/owin-1.0.html）。微软已经创建了Katana项目，该项目是OWIN标准的实现，并提供了一组组件，这些组件提供了Web应用程序所需的功能。让微软感兴趣的是OWIN/Katana将ASP.NET技术堆栈从.NET框架的其余部分独立了出来，这带来了更大的修改速率（译者对OWIN还没太了解，这可能是指若按照OWIN的方式开发应用程序，可以使应用程序更易于修改——译者注）。

OWIN developers select the services that they require for their application, rather than consuming an entire platform as happens now with ASP.NET. Individual services—known as middleware in the OWIN terminology—can be developed at different rates, and developers will be able to choose between providers for different services, rather than being tied to a Microsoft implementation.
OWIN开发人员为他们的应用程序选择所需的服务，而不是像现在这样单纯地使用ASP.NET平台。个别服务——在OWIN术语中称为“Middleware（中间件）”——可能会有不同的开发速率，而开发人员将能够在不同的服务提供商之间进行选择，而不是被绑定在微软实现上。

There is a lot to like about the direction that OWIN and Katana are heading in, but it is in the early days, and it will be some time before it becomes a complete platform for ASP.NET applications. As I write this, it is possible to build Web API and SignalR applications without needing the System.Web namespace or IIS to process requests, but that's about all. The MVC framework requires the standard ASP.NET platform and will continue to do so for some time to come.
OWIN和Katana有很多喜欢发展的方向，但它仍处于早期时期，还需要一段时间才能成为ASP.NET应用程序的完整平台。在我编写本书的时候，它已可以在不需要System.Web命名空间或者IIS处理请求的情况下，建立Web API和SignalR应用程序了。MVC框架需要标准的ASP.NET平台，因此在一段时间内仍将沿用现在的做法。

The ASP.NET platform and IIS are not going away. Microsoft has been clear that it sees one of the most attractive aspects of OWIN as allowing developers more flexibility in which middleware components are hosted by IIS, and Project Katana already has support for the System.Web namespaces. OWIN and Katana are not the end of ASP.NET—rather, they represent an evolution where Microsoft allows developers more flexibility in how ASP.NET applications are assembled and executed.
ASP.NET平台以及IIS不会消失。微软已经清楚地看到，OWIN最有吸引力的一个方面是开发者具有了更大的灵活性，中间组件可以由IIS来托管，而Katana项目已经实现了对System.Web命名空间的支持。OWIN和Katana不是ASP.NET的终结——而是预示着一种变革，微软让开发人员能够在ASP.NET应用程序的编译和执行方面更加灵活。

OWIN and Katana won't have a major impact on MVC framework developers for some time, but changes are already taking effect—and one of these is that ASP.NET Identity is implemented as an OWIN middleware component. This isn't ideal because it means that MVC framework applications have to mix OWIN and traditional ASP.NET platform techniques to use Identity, but it isn't too burdensome once you understand the basics and know how to get OWIN set up, which I demonstrate in the sections that follow.
OWIN和Katana在一段时间内还不会对MVC框架开发人员发生重大冲击，但变化正在发生——其中之一便是ASP.NET Identity要作为OWIN中间件而实现。这种情况不太理想，因为这意味着，MVC框架的应用程序为了使用Identity，必须将OWIN和传统的ASP.NET平台混搭在一起，这太烦琐了，在你理解了基本概念并且知道如何建立OWIN（以下几小节演示）之后，便会明白。

13.2.1 Creating the ASP.NET Identity Database
13.2.1 创建ASP.NET Identity数据库

ASP.NET Identity isn't tied to a SQL Server schema in the same way that Membership was, but relational storage is still the default—and simplest—option, and it is the one that I will be using in this chapter. Although the NoSQL movement has gained momentum in recent years, relational databases are still the mainstream storage choice and are well-understood in most development teams.
ASP.NET Identity并未像Membership那样，被绑定到SQL Server架构，但关系型存储仍是默认的，而且是最简单的选择，这也是本章中将使用的形式。虽然近年来出现了NoSQL运动势头，但关系型数据库仍然是主要的存储选择，而且大多数开发团队都有良好理解。

ASP.NET Identity uses the Entity Framework Code First feature to automatically create its schema, but I still need to create the database into which that schema—and the user data—will be placed, just as I did in Chapter 10 when I created the database for session state data (the universal provider that I used to manage the database uses the same Code First feature).
ASP.NET Identity使用Entity Framework的Code First特性自动地创建它的数据架构（Schema），但我仍然需要创建一个用来放置此数据架构以及用户数据的数据库，就像第10章所做的那样，当时为会话状态数据创建了数据库（用来管理数据库的通用提供器同样使用了Code First特性）。

As in Chapter 10, I will be using the localdb feature to create my database. As a reminder, localdb is included in Visual Studio and is a cut-down version of SQL Server that allows developers to easily create and work with databases.
正如第10章那样，我将使用localdb特性来创建数据库。要记住的是，localdb是包含在Visual Studio之中的，而且是一个简化版的SQL Server，能够让开发者方便地创建和使用数据库。

Select SQL Server Object Explorer from the Visual Studio View menu and right-click the SQL Server object in the window that appears. Select Add SQL Server from the pop-up menu, as shown in Figure 13-2.
从Visual Studio的“View（视图）”菜单中选择“SQL Server Object Explorer（SQL Server对象资源管理器）”，并在所出现的窗口中右击“SQL Server”对象。从弹出菜单选择“Add SQL Server（添加SQL Server）”，如图13-2所示。

Visual Studio will display the Connect to Server dialog. Set the server name to (localdb)\v11.0, select the Windows Authentication option, and click the Connect button. A connection to the database will be established and shown in the SQL Server Object Explorer window. Expand the new item, right-click Databases, and select Add New Database from the pop-up window, as shown in Figure 13-3.
Visual Studio将显示“Connect to Server（连接到服务器）”对话框，将服务器名称设置为(localdb)\v11.0，选择“Windows Authentication（Windows认证）”选项，点击“Connect（连接）”按钮。这将建立一个数据库连接，并显示在“SQL Server对象资源管理器”窗口中。展开这个新项，右击“Databases（数据库）”，并从弹出菜单选择“Add New Database（添加新数据库）”，如图13-3所示。

Set the Database Name option to IdentityDb, leave the Database Location value unchanged, and click the OK button to create the database. The new database will be shown in the Databases section of the SQL connection in the SQL Server Object Explorer.
将“Database Name（数据库名称）”选项设置为“IdentityDb”，不用改变“Database Location（数据库位置）”的值，点击OK按钮创建此数据库。这个新数据库将出现在“SQL Server对象资源管理器”中“SQL连接”的“数据库”小节中。

13.2.2 Adding the Identity Packages
13.2.2 添加Identity包

Identity is published as a set of NuGet packages, which makes it easy to install them into any project. Enter the following commands into the Package Manager Console:
Identity是作为一组NuGet包发布的，因此易于将其安装到任何项目。请在“Package Manager Console（包管理器控制台）”中输入以下命令：

Install-Package Microsoft.AspNet.Identity.EntityFramework –Version 2.0.0(2.2.1)
Install-Package Microsoft.AspNet.Identity.OWIN -Version 2.0.0(2.2.1)
Install-Package Microsoft.Owin.Host.SystemWeb -Version 2.1.0(3.0.1)

Visual Studio can create projects that are configured with a generic user account management configuration, using the Identity API. You can add the templates and code to a project by selecting the MVC template when creating the project and setting the Authentication option to Individual User Accounts. I don't use the templates because I find them too general and too verbose and because I like to have direct control over the contents and configuration of my projects. I recommend you do the same, not least because you will gain a better understanding of how important features work, but it can be interesting to look at the templates to see how common tasks are performed.
Visual Studio能够创建一些使用Identity API的项目，这种项目以“泛型用户账号管理配置”进行配置。你可以给项目添加一些模板和代码，只需在创建项目时选择MVC模板，并将认证选项设置为Individual User Accounts（个别用户账号）。我没有使用这种模板，因为我发现它们太普通，也太混乱，而且我喜欢对我项目中的内容和配置有直接的控制。我建议你也这么做，这不仅让你能够对重要特性的工作机制获得更好的理解，而且，考察模板如何执行常规任务也是有趣的。

13.2.3 Updating the Web.config File
13.2.3 更新Web.config文件

Two changes are required to the Web.config file to prepare a project for ASP.NET Identity. The first is a connection string that describes the database I created in the previous section. The second change is to define an application setting that names the class that initializes OWIN middleware and that is used to configure Identity. Listing 13-4 shows the changes I made to the Web.config file. (I explained how connection strings and application settings work in Chapter 9.)
为了做好项目使用ASP.NET Identity的准备，需要在Web.config文件中做两处修改。第一处是连接字符串，它描述了我在上一小节中创建的数据库。第二处修改是定义一个应用程序设置，它命名对OWIN中间件进行初始化的类，并将它用于配置Identity。清单显示了对Web.config文件的修改（第9章已经解释过连接字符串和应用程序设置）。

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
        <section name="entityFramework"
            type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection,
            EntityFramework, Version=6.0.0.0, Culture=neutral,
            PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    </configSections> 
    <connectionStrings>
        <add name="IdentityDb" providerName="System.Data.SqlClient"
            connectionString="Data Source=(localdb)\v11.0;
                Initial Catalog=IdentityDb;
                Integrated Security=True;
                Connect Timeout=15;
                Encrypt=False;TrustServerCertificate=False;
                MultipleActiveResultSets=True"/>
    </connectionStrings> 

    <appSettings>
        <add key="webpages:Version" value="3.0.0.0" />
        <add key="webpages:Enabled" value="false" />
        <add key="ClientValidationEnabled" value="true" />
        <add key="UnobtrusiveJavaScriptEnabled" value="true" />
        <add key="owin:AppStartup" value="Users.IdentityConfig" /> 
    </appSettings>
    <system.web>
        <compilation debug="true" targetFramework="4.5.1" />
        <httpRuntime targetFramework="4.5.1" />
    </system.web>
    <entityFramework>
        <defaultConnectionFactory
            type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory,
            EntityFramework">
        <parameters>
            <parameter value="v11.0" />
        </parameters>
    </defaultConnectionFactory>
    <providers>
        <provider invariantName="System.Data.SqlClient"
            type="System.Data.Entity.SqlServer.SqlProviderServices,
            EntityFramework.SqlServer" />
        </providers>
    </entityFramework>
</configuration>

OWIN defines its own application startup model, which is separate from the global application class that I described in Chapter 3. The application setting, called owin:AppStartup, specifies a class that OWIN will instantiate when the application starts in order to receive its configuration.
OWIN定义了它自己的应用程序启动模型，与第3章所描述的全局应用程序类是分开的。上述的应用程序设置，名称为owin:AppStartup，指定了应用程序启动时，将由OWIN进行实例化的类，目的是接受它的配置。

13.2.4 Creating the Entity Framework Classes
13.2.4 创建Entity Framework类

If you have used Membership in projects, you may be surprised by just how much initial preparation is required for ASP.NET Identity. The extensibility that Membership lacked is readily available in ASP.NET Identity, but it comes with a price of having to create a set of implementation classes that the Entity Framework uses to manage the database. In the sections that follow, I’ll show you how to create the classes needed to get Entity Framework to act as the storage system for ASP.NET Identity.
如果你曾在项目使用过Membership，可能会感觉奇怪，ASP.NET Identity需要的初始化准备怎么这么多。在ASP.NET Identity中可以轻易地使用Membership所缺乏的可扩展性，但其代价是需要创建一组实现类，由Entity Framework用于管理数据库。在以下小节中，我将演示如何创建所需要的这些类，以便让Entity Framework将它们用于ASP.NET Identity的存储系统。

1. Creating the User Class
1. 创建用户类

The first class to define is the one that represents a user, which I will refer to as the user class. The user class is derived from IdentityUser, which is defined in the Microsoft.AspNet.Identity.EntityFramework namespace. IdentityUser provides the basic user representation, which can be extended by adding properties to the derived class, which I describe in Chapter 15. Table 13-2 shows the built-in properties that IdentityUser defines, which are the ones I will be using in this chapter.
第一个要定义的类是表现一个用户的类，我将它称为“User Class（用户类）”。这个用户类派生于IdentityUser，它是在Microsoft.AspNet.Identity.EntityFramework命名空间中定义的。IdentityUser提供了基本的用户表示，可以通过在它派生的类中添加属性的办法，对这个类进行扩展，我会在第15章中对此进行描述。表13-2列出了IdentityUser所定义的内建属性（现在流行将“内建（Built-in）”说成“内置”，但我不会人云亦云，这两者在含义上是有区别的，“内建”完全是自己创建的，而“内置”有可能是别人做的东西拿来放入其中的——译者注），本章将使用这些属性。

What is important at the moment is that the IdentityUser class provides access only to the basic information about a user: the use's name, e-mail, phone, password hash, role memberships, and so on. If I want to store any additional information about the user, I have to add properties to the class that I derive from IdentityUser and that will be used to represent users in my application. I demonstrate how to do this in Chapter 15.
目前最重要的是这个IdentityUser类只提供了对用户基本信息的访问：用户名、E-mail、电话、哈希口令、角色成员等等。如果希望存储用户的各种附加信息，就需要在IdentityUser派生的类上添加属性，并将它用于表示应用程序中的用户，第15章中将演示其做法。

To create the user class for my application, I created a class file called AppUserModels.cs in the Models folder and used it to create the AppUser class, which is shown in Listing 13-5.
为了创建应用程序中的用户类，我在Models文件夹中创建了一个类文件，名称为AppUserModels.cs（注意，这个文件名称错了，应当是AppUser.cs），并用它创建了AppUser类，这个类如清单13-5所示。

using System;
using Microsoft.AspNet.Identity.EntityFramework; 

namespace Users.Models {

    public class AppUser : IdentityUser {
        // additional properties will go here
        // 这里将放置附加属性
    }
}

That's all I have to do at the moment, although I'll return to this class in Chapter 15, when I show you how to add application-specific user data properties.
以上便是此刻要做的全部工作，第15章会再次讨论这个类，那时会演示如何添加应用程序专用的用户数据属性。

2. Creating the Database Context Class
2. 创建数据库上下文类

The next step is to create an Entity Framework database context that operates on the AppUser class. This will allow the Code First feature to create and manage the schema for the database and provide access to the data it stores. The context class is derived from IdentityDbContext<T>, where T is the user class (AppUser in the example). I created a folder called Infrastructure in the project and added to it a class file called AppIdentityDbContext.cs, the contents of which are shown in Listing 13-6.
下一个步骤是创建Entity Framework数据库的上下文，用于对AppUser类进行操作。这可以用Code First特性来创建和管理数据架构，并对数据库所存储的数据进行访问。这个上下文类派生于IdentityDbContext<T> ，其中的T是用户类（即此例中的AppUser）。我在项目中创建了一个文件夹，名称为Infrastructure，并在其中添加了一个类文件，名称为AppIdentityDbContext.cs，其内容如清单13-6所示。

using System.Data.Entity;
using Microsoft.AspNet.Identity.EntityFramework;
using Users.Models; 

namespace Users.Infrastructure {
    public class AppIdentityDbContext : IdentityDbContext<AppUser> {

        public AppIdentityDbContext() : base("IdentityDb") { }

        static AppIdentityDbContext() {
            Database.SetInitializer<AppIdentityDbContext>(new IdentityDbInit());
        }

        public static AppIdentityDbContext Create() {
            return new AppIdentityDbContext();
        }
    }

    public class IdentityDbInit
            : DropCreateDatabaseIfModelChanges<AppIdentityDbContext> {

        protected override void Seed(AppIdentityDbContext context) {
            PerformInitialSetup(context);
            base.Seed(context);
        }

        public void PerformInitialSetup(AppIdentityDbContext context) {
            // initial configuration will go here
            // 初始化配置将放在这儿
        }
    }
}

The constructor for the AppIdentityDbContext class calls its base with the name of the connection string that will be used to connect to the database, which is IdentityDb in this example. This is how I associate the connection string I defined in Listing 13-4 with ASP.NET Identity.
这个AppIdentityDbContext类的构造器调用了它的基类，其参数是连接字符串的名称，IdentityDb，用于与数据库连接。这是让清单13-4定义的连接字符串与ASP.NET Identity联结起来的方法。

The AppIdentityDbContext class also defines a static constructor, which uses the Database.SetInitializer method to specify a class that will seed the database when the schema is first created through the Entity Framework Code First feature. My seed class is called IdentityDbInit, and I have provided just enough of a class to create a placeholder so that I can return to seeding the database later by adding statements to the PerformInitialSetup method. I show you how to seed the database in Chapter 14.
这个AppIdentityDbContext类还定义了一个静态的构造器，它使用Database.SetInitializer方法指定了一个种植数据库的类（种植数据库的含义是往数据库中植入数据的意思，说穿了，就是用一些数据对数据库进行初始化——译者注），当通过Entity Framework的Code First特性第一次创建数据库架构时，会用到这个类。这个种植类叫做IdentityDbInit，而且我已经提供了一个类，创建了一个占位符，后面可以回过头来在PerformInitialSetup方法中添加语句，就可以种植数据库了。第14章将演示如何种植数据库。

Finally, the AppIdentityDbContext class defines a Create method. This is how instances of the class will be created when needed by the OWIN, using the class I describe in the “Creating the Start Class” section.
最后，AppIdentityDbContext类定义了一个Create方法。这是由OWIN在必要时创建类实例的办法，这个由OWIN使用的类将在“创建启动类”中进行描述。

3. Creating the User Manager Class
3. 创建用户管理器类

One of the most important Identity classes is the user manager, which manages instances of the user class. The user manager class must be derived from UserManager<T> , where T is the user class. The UserManager<T> class isn't specific to the Entity Framework and provides more general features for creating and operating on user data. Table 13-3 shows the basic methods and properties defined by the UserManager<T> class for managing users. There are others, but rather than list them all here, I'll describe them in context when I describe the different ways in which user data can be managed.
最重要的Identity类之一是“User Manager（用户管理器）”，用来管理用户类实例。用户管理器类必须派生于UserManager<T> ，其中T是用户类。这个UserManager<T> 类并非是专用于Entity Framework的，而且它提供了很多通用特性，用以创建用户并对用户数据进行操作。表13-3列出了UserManager<T> 类为管理用户而定义的基本方法和操作。还有一些其他方法，这里并未全部列出来，我会在适当的情形下对它们进行描述，那时会介绍管理用户数据的不同方式。

I added a class file called AppUserManager.cs to the Infrastructure folder and used it to define the user manager class, which I have called AppUserManager, as shown in Listing 13-7.
我在Infrastructure文件夹中添加了一个类文件，名称为AppUserManager.cs，用它定义了用户管理器类，名称为AppUserManager，如清单13-7所示。

using Microsoft.AspNet.Identity;
using Microsoft.AspNet.Identity.EntityFramework;
using Microsoft.AspNet.Identity.Owin;
using Microsoft.Owin;
using Users.Models; 

namespace Users.Infrastructure {
    public class AppUserManager : UserManager<AppUser> {

        public AppUserManager(IUserStore<AppUser> store)
                : base(store) {
        }

        public static AppUserManager Create(
                IdentityFactoryOptions<AppUserManager> options,
                IOwinContext context) {
            AppIdentityDbContext db = context.Get<AppIdentityDbContext>();
            AppUserManager manager = new AppUserManager(new UserStore<AppUser>(db));
            return manager;
        }
    }
}

The static Create method will be called when Identity needs an instance of the AppUserManager, which will happen when I perform operations on user data—something that I will demonstrate once I have finished performing the setup.
在Identity需要一个AppUserManager的实例时，将会调用静态的Create方法，这种情况将在对用户数据执行操作时发生——也是在完成设置之后要演示的事情。

To create an instance of the AppUserManager class, I need an instance of UserStore<AppUser> . The UserStore<T> class is the Entity Framework implementation of the IUserStore<T> interface, which provides the storage-specific implementation of the methods defined by the UserManager class. To create the UserStore<AppUser> , I need an instance of the AppIdentityDbContext class, which I get through OWIN as follows:
为了创建AppUserManager类的实例，我需要一个UserStore<AppUser> 实例。这个UserStore<T> 类是IUserStore<T> 接口的Entity Framework实现，它提供了UserManager类所定义的存储方法的实现。为了创建UserStore<AppUser> ，又需要AppIdentityDbContext类的一个实例，这是通过OWIN按如下办法得到的：

...
AppIdentityDbContext db = context.Get<AppIdentityDbContext>();
...

The IOwinContext implementation passed as an argument to the Create method defines a generically typed Get method that returns instances of objects that have been registered in the OWIN start class, which I describe in the following section.
被作为参数传递给Create方法的IOwinContext实现定义了一个泛型的Get方法，它会返回已经在OWIN启动类中注册的对象实例，启动类在以下小节描述。

4. Creating the Start Class
4. 创建启动类

The final piece I need to get ASP.NET Identity up and running is a start class. In Listing 13-4, I defined an application setting that specified a configuration class for OWIN, like this:
为了使ASP.NET Identity就绪并能运行，要做的最后一个片段是Start Class（启动类）。在清单13-4中，我定义了一个应用程序设置，它为OWIN指定配置类，如下所示：

...
<add key="owin:AppStartup" value="Users.IdentityConfig" />
...

OWIN emerged independently of ASP.NET and has its own conventions. One of them is that there is a class that is instantiated to load and configure middleware and perform any other configuration work that is required. By default, this class is called Start, and it is defined in the global namespace. This class contains a method called Configuration, which is called by the OWIN infrastructure and passed an implementation of the Owin.IAppBuilder interface, which supports setting up the middleware that an application requires. The Start class is usually defined as a partial class, with its other class files dedicated to each kind of middleware that is being used.
OWIN是独立出现在ASP.NET中的，并且有它自己的约定。其中之一就是，为了加载和配置中间件，并执行所需的其他配置工作，需要有一个被实例化的类。默认情况下，这个类叫做Start，而且是在全局命名空间中定义的。这个类含有一个名称为Configuration的方法，该方法由OWIN基础架构进行调用，并为该方法传递一个Owin.IAppBuilder接口的实现，由它支持应用程序所需中间件的设置。Start类通常被定义成分部类，还有一些其他的类文件，它们分别专用于要用的每一种中间件。

I freely ignore this convention, given that the only OWIN middleware that I use in MVC framework applications is Identity. I prefer to use the application setting in the Web.config file to define a single class in the top-level namespace of the application. To this end, I added a class file called IdentityConfig.cs to the App_Start folder and used it to define the class shown in Listing 13-8, which is the class that I specified in the Web.config folder.
我随意地忽略了这一约定，因为我在MVC框架应用程序中使用的唯一OWIN中间件就是Identity。为了在应用程序的顶级命名空间定义一个类，我喜欢在Web.config文件中使用应用程序设置。于是我在App_Start文件夹中添加了一个类文件，名称为IdentityConfig.cs，并用它定义了如清单13-8所示的类，这是我在Web.config文件中指定的一个类。

using Microsoft.AspNet.Identity;
using Microsoft.Owin;
using Microsoft.Owin.Security.Cookies;
using Owin;
using Users.Infrastructure; 

namespace Users {
    public class IdentityConfig {
        public void Configuration(IAppBuilder app) {

            app.CreatePerOwinContext<AppIdentityDbContext>(AppIdentityDbContext.Create);
            app.CreatePerOwinContext<AppUserManager>(AppUserManager.Create); 

            app.UseCookieAuthentication(new CookieAuthenticationOptions {
                AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
                    LoginPath = new PathString("/Account/Login"),
            });
        }
    }
}

The IAppBuilder interface is supplemented by a number of extension methods defined in classes in the Owin namespace. The CreatePerOwinContext method creates a new instance of the AppUserManager and AppIdentityDbContext classes for each request. This ensures that each request has clean access to the ASP.NET Identity data and that I don't have to worry about synchronization or poorly cached database data.
IAppBuilder接口是由一些扩展方法提供的，这些扩展方法的定义在Owin命名空间的一些类中。CreatePerOwinContext用于创建AppUserManager的新实例，AppIdentityDbContext类用于每一个请求。这样保证每一个请求对ASP.NET Identity数据有清晰的访