实施

• 创建身份验证服务

  要创建身份验证服务，请打开一个终端，然后执行以下命令：

  amplify add auth
  
  ? Do you want to use the default authentication and security configuration? Select Default configuration with Social Provider and press enter
  ? How do you want users to be able to sign in? Select the default Username and press enter
  ? Do you want to configure advanced settings? Select the default No, I am done and press enter
  ? What domain name prefix do you want to use? Select the default and press enter
  Enter your redirect signin URI: type gettingstarted:// and press enter
  ? Do you want to add another redirect signin URI? Select the default N and press enter
  Enter your redirect signout URI: type gettingstarted:// and press enter
  ? Do you want to add another redirect signout URI? Select the default N and press enter
  ? Select the social providers you want to configure for your user pool: do not select any provider and press enter

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  当您看到此消息时，即表示配置成功（资源的确切名称将有所不同）：

  Successfully added resource iosgettingstartedfc5a4717 locally

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• 部署身份验证服务

  现在，已在本地配置身份验证服务，我们可以将它部署到云：在终端中，请在项目目录中执行以下命令：
  

  amplify push
  
  # press Y when asked to continue

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  片刻之后，您应看到以下消息：
  

  ✔ All resources are updated in the cloud
  
  Hosted UI Endpoint: https://iosgettingstarted-dev.auth.eu-central-1.amazoncognito.com/
  Test Your Hosted UI Endpoint: https://iosgettingstarted-dev.auth.eu-central-1.amazoncognito.com/login?response_type=code&client_id=1234567890&redirect_uri=gettingstarted://

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• 向项目添加 Amplify 身份验证库

  在转至代码之前，请将 Amplify 身份验证库添加到项目的依赖项中。打开 Podfile 文件，然后使用 AmplifyPlugins/AWSCognitoAuthPlugin 添加行，或者复制并粘贴以下整个文件
  

  # you need at least version 13.0 for this tutorial, more recent versions are valid too
  platform :ios, '13.0'
  
  target 'getting started' do
    # Comment the next line if you don't want to use dynamic frameworks
    use_frameworks!
  
    # Pods for getting started
    pod 'Amplify', '~> 1.0'                             # required amplify dependency
    pod 'Amplify/Tools', '~> 1.0'                       # allows to call amplify CLI from within Xcode
  
    pod 'AmplifyPlugins/AWSCognitoAuthPlugin', '~> 1.0' # support for Cognito user authentication
  
  end

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  在终端执行以下命令：

  pod install

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  该命令需要几秒钟才能完成。您将看到（实际版本号可能有所不同）：

  Analyzing dependencies
  Downloading dependencies
  Installing AWSAuthCore (2.14.1)
  Installing AWSCognitoIdentityProvider (2.14.1)
  Installing AWSCognitoIdentityProviderASF (1.0.1)
  Installing AWSCore (2.14.1)
  Installing AWSMobileClient (2.14.1)
  Installing AWSPluginsCore (1.0.4)
  Installing AmplifyPlugins (1.0.4)
  Generating Pods project
  Integrating client project
  Pod installation complete! There are 3 dependencies from the Podfile and 8 total pods installed.

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• 在运行时配置 Amplify 身份验证库

  返回到 Xcode，打开 Backend.swift 文件。在后端类中，

  • 为 AmplifyPlugins 添加导入语句
  • 向上一节中添加的 Amplify 初始化代码中添加一行。

  完整代码块应如下所示：

  // at the top of the file
  import AmplifyPlugins
  
  private init () {
    // initialize amplify
    do {
       try Amplify.add(plugin: AWSCognitoAuthPlugin())
       try Amplify.configure()
       print("Initialized Amplify")
    } catch {
       print("Could not initialize Amplify: \(error)")
    }
  }

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  要验证一切是否都按预期运行，请构建项目。单击 Product 菜单，然后选择 Build，或按 ⌘B。应该不会出现错误。

• 在运行时触发身份验证

  其余代码更改会跟踪用户的状态（他们是否已登录？）并在用户未登录时触发登录/注册用户界面。 

  a.添加登录和注销代码。在后端类中的任意位置，添加以下三种方法：

   

  // MARK: - User Authentication
  
  // signin with Cognito web user interface
  public func signIn() {
  
      _ = Amplify.Auth.signInWithWebUI(presentationAnchor: UIApplication.shared.windows.first!) { result in
          switch result {
          case .success(_):
              print("Sign in succeeded")
          case .failure(let error):
              print("Sign in failed \(error)")
          }
      }
  }
  
  // signout
  public func signOut() {
  
      _ = Amplify.Auth.signOut() { (result) in
          switch result {
          case .success:
              print("Successfully signed out")
          case .failure(let error):
              print("Sign out failed with error \(error)")
          }
      }
  }
  
  // change our internal state, this triggers an UI update on the main thread
  func updateUserData(withSignInStatus status : Bool) {
      DispatchQueue.main.async() {
          let userData : UserData = .shared
          userData.isSignedIn = status
      }
  }

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  b.添加身份验证中心侦听器

  为了跟踪身份验证状态的变化，我们添加了代码以订阅由 Amplify 发送的身份验证事件。我们在 Backend.init() 方法中初始化该中心。

  在收到身份验证事件时，我们将调用 updateUserData() 方法。此方法可使 UserData 对象保持同步。UserData.isSignedIn 属性为 @Published，这意味着当值更改时，用户界面会自动刷新。 

  我们还添加了代码以在应用程序启动时检查以前的身份验证状态。当应用程序启动时，它会检查 Cognito 会话是否已存在，并相应地更新 UI。

  在 Backend.init() 中，请在 Amplify 初始化后添加以下代码：

  // in private init() function
  // listen to auth events.
  // see https://github.com/aws-amplify/amplify-ios/blob/master/Amplify/Categories/Auth/Models/AuthEventName.swift
  _ = Amplify.Hub.listen(to: .auth) { (payload) in
  
      switch payload.eventName {
  
      case HubPayload.EventName.Auth.signedIn:
          print("==HUB== User signed In, update UI")
          self.updateUserData(withSignInStatus: true)
  
      case HubPayload.EventName.Auth.signedOut:
          print("==HUB== User signed Out, update UI")
          self.updateUserData(withSignInStatus: false)
  
      case HubPayload.EventName.Auth.sessionExpired:
          print("==HUB== Session expired, show sign in UI")
          self.updateUserData(withSignInStatus: false)
  
      default:
          //print("==HUB== \(payload)")
          break
      }
  }
   
  // let's check if user is signedIn or not
   _ = Amplify.Auth.fetchAuthSession { (result) in
       do {
           let session = try result.get()
                  
  // let's update UserData and the UI
       self.updateUserData(withSignInStatus: session.isSignedIn)
                  
       } catch {
            print("Fetch auth session failed with error - \(error)")
      }
  }    

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  c.更新用户界面代码

  代码中的最后一个更改与用户界面相关，我们将 ZStack 添加到 ContentView。根据 UserData.isSignedIn 的值，UI 将显示 SigninButton 或主列表视图。

  打开 ContentView.swift 并替换 ContentView 结构中的正文：
  

  var body: some View {
  
      ZStack {
          if (userData.isSignedIn) {
              NavigationView {
                  List {
                      ForEach(userData.notes) { note in
                          ListRow(note: note)
                      }
                  }
                  .navigationBarTitle(Text("Notes"))
                  .navigationBarItems(leading: SignOutButton())
              }
          } else {
              SignInButton()
          }
      }
  }

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  在同一文件中，添加 SignInButton 和 SignOutButton 视图：

  struct SignInButton: View {
      var body: some View {
          Button(action: { Backend.shared.signIn() }){
              HStack {
                  Image(systemName: "person.fill")
                      .scaleEffect(1.5)
                      .padding()
                  Text("Sign In")
                      .font(.largeTitle)
              }
              .padding()
              .foregroundColor(.white)
              .background(Color.green)
              .cornerRadius(30)
          }
      }
  }
  
  struct SignOutButton : View {
      var body: some View {
          Button(action: { Backend.shared.signOut() }) {
                  Text("Sign Out")
          }
      }
  }

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  要验证一切是否都按预期运行，请构建项目。单击 Product 菜单，然后选择 Build，或按 ⌘B。应该不会出现错误。
  

  d.更新 Info.plist

  最后，我们必须确保在 Cognito 托管用户界面提供的 Web 身份验证序列结束时启动我们的应用程序。我们将 gettingstarted URI 方案添加到应用程序的 Info.plist 文件中。

  在 Xcode 中，选择 Info.plist 文件，右键单击该文件，然后选择“打开为源代码”。
  

  

  在顶部 <dict> 元素内添加以下 <key> 和 <array> 元素。

  <plist version="1.0">
  
      <dict>
      <!-- YOUR OTHER PLIST ENTRIES HERE -->
  
      <!-- ADD AN ENTRY TO CFBundleURLTypes for Cognito Auth -->
      <!-- IF YOU DO NOT HAVE CFBundleURLTypes, YOU CAN COPY THE WHOLE BLOCK BELOW -->
      <key>CFBundleURLTypes</key>
      <array>
          <dict>
              <key>CFBundleURLSchemes</key>
              <array>
                  <string>gettingstarted</string>
              </array>
          </dict>
      </array>
  
      <!-- ... -->
      </dict>

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  e.构建和测试

  要验证一切是否都按预期运行，请构建项目。单击 Product 菜单，然后选择 Run，或按 ⌘R。应该不会出现错误。应用程序将在“登录”按钮上启动。

  以下是完整的注册流程：