I will be using the AppUserManager class repeatedly in the Account controller, so I defined a property called UserManager that returns the instance of the class using the GetOwinContext extension method for the HttpContext class, just as I did for the Admin controller in Chapter 13.
我会在Account控制器中反复使用AppUserManager类，因此定义了一个名称为的UserManager属性，它使用HttpContext类的GetOwinContext扩展方法来返回AppUserManager类的实例。

The FindAsync method takes the account name and password supplied by the user and returns an instance of the user class (AppUser in the example application) if the user account exists and if the password is correct. If there is no such account or the password doesn’t match the one stored in the database, then the FindAsync method returns null, in which case I add an error to the model state that tells the user that something went wrong.
FindAsync方法以用户提供的账号名和口令为参数，并在该用户账号存在且口令正确时，返回一个用户类（此例中的AppUser）的实例。如果无此账号，或者与数据库存储的不匹配，那么FindAsync方法返回空（null），出现这种情况时，我给模型状态添加了一条错误消息，告诉用户可能出错了。

If the FindAsync method does return an AppUser object, then I need to create the cookie that the browser will send in subsequent requests to show they are authenticated. Here are the relevant statements:
如果FindAsync方法确实返回了AppUser对象，那么则需要创建Cookie，浏览器会在后继的请求中发送这个Cookie，表明他们是已认证的。以下是有关语句：

... ClaimsIdentity ident = await UserManager.CreateIdentityAsync(user, DefaultAuthenticationTypes.ApplicationCookie); AuthManager.SignOut(); AuthManager.SignIn(new AuthenticationProperties {IsPersistent = false}, ident); return Redirect(returnUrl); ...

The first step is to create a ClaimsIdentity object that identifies the user. The ClaimsIdentity class is the ASP.NET Identity implementation of the IIdentity interface that I described in Table 14-4 and that you can see used in the “Using Roles for Authorization” section later in this chapter.
第一步是创建一个标识该用户的ClaimsIdentity对象。ClaimsIdentity类是表14-4所描述的IIdentity接口的ASP.NET Identity实现，可以在本章稍后的“使用角色授权”小节中看到它的使用。

Tip Don’t worry about why the class is called ClaimsIdentity at the moment. I explain what claims are and how they can be used in Chapter 15.
提示：此刻不必关心这个类为什么要调用ClaimsIdentity，第15章会解释什么是声明（Claims），并介绍如何使用它们。

Instances of ClaimsIdentity are created by calling the user manager CreateIdentityAsync method, passing in a user object and a value from the DefaultAuthenticationTypes enumeration. The ApplicationCookie value is used when working with individual user accounts.
ClaimsIdentity的实例是调用用户管理器的CreateIdentityAsync方法而创建的，在其中传递了一个用户对象和DefaultAuthenticationTypes枚举中的一个值。在使用个别用户账号进行工作时，会用到ApplicationCookie值。

The next step is to invalidate any existing authentication cookies and create the new one. I defined the AuthManager property in the controller because I’ll need access to the object it provides repeatedly as I build the functionality in this chapter. The property returns an implementation of the IAuthenticationManager interface that is responsible for performing common authentication options. I have described the most useful methods provided by the IAuthenticationManager interface in Table 14-5.
下一个步骤是让已认证的Cookie失效，并创建一个新的Cookie。我在该控制器中定义了AuthManager属性，因为在建立本章功能过程中，需要反复访问它所提供的对象。该属性返回的是IAuthenticationManager接口的实现，它负责执行常规的认证选项。表14-5中描述了IAuthenticationManager接口所提供的最有用的方法。

Table 14-5. The Most Useful Methods Defined by the IAuthenticationManager Interface
表14-5. IAuthenticationManager接口定义的最有用的方法

Name
名称 Description
描述

SignIn(options, identity) Signs the user in, which generally means creating the cookie that identifies authenticated requests
签入用户，这通常意味着要创建用来标识已认证请求的Cookie

SignOut() Signs the user out, which generally means invalidating the cookie that identifies authenticated requests
签出用户，这通常意味着使标识已认证用户的Cookie失效