使用 WebView 进行用户身份验证

本文档介绍如何将凭据管理器 API 与使用 WebView 的 Android 应用集成。

概述

在深入了解集成过程之前，务必了解原生 Android 代码、在 WebView 中呈现的管理应用身份验证的 Web 组件以及后端之间的通信流程。此流程涉及注册（创建凭据）和身份验证（获取现有凭据）。

注册（创建密码键）

  1. 后端会生成初始注册 JSON 并将其发送到在 WebView 中呈现的网页。
  2. 网页使用navigator.credentials.create() 来注册新的凭据。您将在后续步骤中使用注入的 JavaScript 覆盖此方法，以将请求发送到 Android 应用。
  3. Android 应用使用凭据管理器 API 来构建凭据请求 并使用它来createCredential。
  4. 凭据管理器 API 与应用共享公钥凭据。
  5. 应用将公钥凭据发送回网页，以便注入的 JavaScript 可以解析响应。
  6. 网页将公钥发送到后端，后端会验证并保存公钥。
Chart showing the passkey registration flow
图 1. 密码键注册流程。

身份验证（获取密码键）

  1. 后端会生成身份验证 JSON 以获取凭据，并将其发送到在 WebView 客户端中呈现的网页。
  2. 网页使用navigator.credentials.get。使用注入的 JavaScript 覆盖此方法，以将请求重定向到 Android 应用。
  3. 应用通过调用getCredential 使用凭据管理器 API 检索凭据。
  4. 凭据管理器 API 将凭据返回到应用。
  5. 应用获取私钥的数字签名，并将其发送到网页，以便注入的 JavaScript 可以解析响应。
  6. 然后，网页将其发送到服务器，服务器使用公钥验证数字签名。
Chart showing the passkey authentication flow
图 2. 密码键身份验证流程。

同样的流程也可用于密码或联合身份系统。

先决条件

要使用凭据管理器 API，请完成凭据管理器指南先决条件部分中概述的步骤，并确保执行以下操作：

JavaScript 通信

为了允许 WebView 中的 JavaScript 和原生 Android 代码相互通信，您需要在两个环境之间发送消息和处理请求。为此，请将自定义 JavaScript 代码注入 WebView。这使您可以修改 Web 内容的行为并与原生 Android 代码进行交互。

JavaScript 注入

以下JavaScript 代码建立了 WebView 和 Android 应用之间的通信。它覆盖了navigator.credentials.create()和navigator.credentials.get()方法，这些方法由WebAuthn API用于前面描述的注册和身份验证流程。

在您的应用程序中使用此 JavaScript 代码的压缩版本。

创建用于密钥的监听器

设置一个PasskeyWebListener类来处理与 JavaScript 的通信。此类应继承自WebViewCompat.WebMessageListener。此类接收来自 JavaScript 的消息并在 Android 应用中执行必要的操作。

Kotlin

// The class talking to Javascript should inherit:
class PasskeyWebListener(
    private val activity: Activity,
    private val coroutineScope: CoroutineScope,
    private val credentialManagerHandler: CredentialManagerHandler
) : WebViewCompat.WebMessageListener

// ... Implementation details

Java

// The class talking to Javascript should inherit:
class PasskeyWebListener implements WebViewCompat.WebMessageListener {

  // Implementation details
  private Activity activity;

  // Handles get/create methods meant for Java:
  private CredentialManagerHandler credentialManagerHandler;

  public PasskeyWebListener(
    Activity activity,
    CredentialManagerHandler credentialManagerHandler
    ) {
    this.activity = activity;
    this.credentialManagerHandler = credentialManagerHandler;
  }

// ... Implementation details
}

在PasskeyWebListener中，实现请求和响应的逻辑，如下节所述。

处理身份验证请求

为了处理 WebAuthn navigator.credentials.create()或navigator.credentials.get()操作的请求，当 JavaScript 代码向 Android 应用发送消息时，将调用PasskeyWebListener类的onPostMessage方法。

Kotlin

class PasskeyWebListener(...)... {
// ...

  /** havePendingRequest is true if there is an outstanding WebAuthn request.
      There is only ever one request outstanding at a time. */
  private var havePendingRequest = false

  /** pendingRequestIsDoomed is true if the WebView has navigated since
      starting a request. The FIDO module cannot be canceled, but the response
      will never be delivered in this case. */
  private var pendingRequestIsDoomed = false

  /** replyChannel is the port that the page is listening for a response on.
      It is valid if havePendingRequest is true. */
  private var replyChannel: ReplyChannel? = null

  /**
  * Called by the page during a WebAuthn request.
  *
  * @param view Creates the WebView.
  * @param message The message sent from the client using injected JavaScript.
  * @param sourceOrigin The origin of the HTTPS request. Should not be null.
  * @param isMainFrame Should be set to true. Embedded frames are not
    supported.
  * @param replyProxy Passed in by JavaScript. Allows replying when wrapped in
    the Channel.
  * @return The message response.
  */
  @UiThread
  override fun onPostMessage(
    view: WebView,
    message: WebMessageCompat,
    sourceOrigin: Uri,
    isMainFrame: Boolean,
    replyProxy: JavaScriptReplyProxy,
  ) {
    val messageData = message.data ?: return
    onRequest(
      messageData,
      sourceOrigin,
      isMainFrame,
      JavaScriptReplyChannel(replyProxy)
    )
  }

  private fun onRequest(
    msg: String,
    sourceOrigin: Uri,
    isMainFrame: Boolean,
    reply: ReplyChannel,
  ) {
    msg?.let {
      val jsonObj = JSONObject(msg);
      val type = jsonObj.getString(TYPE_KEY)
      val message = jsonObj.getString(REQUEST_KEY)

      if (havePendingRequest) {
        postErrorMessage(reply, "The request already in progress", type)
        return
      }

      replyChannel = reply
      if (!isMainFrame) {
        reportFailure("Requests from subframes are not supported", type)
        return
      }
      val originScheme = sourceOrigin.scheme
      if (originScheme == null || originScheme.lowercase() != "https") {
        reportFailure("WebAuthn not permitted for current URL", type)
        return
      }

      // Verify that origin belongs to your website,
      // it's because the unknown origin may gain credential info.
      if (isUnknownOrigin(originScheme)) {
        return
      }

      havePendingRequest = true
      pendingRequestIsDoomed = false

      // Use a temporary "replyCurrent" variable to send the data back, while
      // resetting the main "replyChannel" variable to null so it’s ready for
      // the next request.
      val replyCurrent = replyChannel
      if (replyCurrent == null) {
        Log.i(TAG, "The reply channel was null, cannot continue")
        return;
      }

      when (type) {
        CREATE_UNIQUE_KEY ->
          this.coroutineScope.launch {
            handleCreateFlow(credentialManagerHandler, message, replyCurrent)
          }

        GET_UNIQUE_KEY -> this.coroutineScope.launch {
          handleGetFlow(credentialManagerHandler, message, replyCurrent)
        }

        else -> Log.i(TAG, "Incorrect request json")
      }
    }
  }

  private suspend fun handleCreateFlow(
    credentialManagerHandler: CredentialManagerHandler,
    message: String,
    reply: ReplyChannel,
  ) {
    try {
      havePendingRequest = false
      pendingRequestIsDoomed = false
      val response = credentialManagerHandler.createPasskey(message)
      val successArray = ArrayList<Any>();
      successArray.add("success");
      successArray.add(JSONObject(response.registrationResponseJson));
      successArray.add(CREATE_UNIQUE_KEY);
      reply.send(JSONArray(successArray).toString())
      replyChannel = null // setting initial replyChannel for the next request
    } catch (e: CreateCredentialException) {
      reportFailure(
        "Error: ${e.errorMessage} w type: ${e.type} w obj: $e",
        CREATE_UNIQUE_KEY
      )
    } catch (t: Throwable) {
      reportFailure("Error: ${t.message}", CREATE_UNIQUE_KEY)
    }
  }

  companion object {
    const val TYPE_KEY = "type"
    const val REQUEST_KEY = "request"
    const val CREATE_UNIQUE_KEY = "create"
    const val GET_UNIQUE_KEY = "get"
  }
}

Java

class PasskeyWebListener implements ... {
// ...

  /**
  * Called by the page during a WebAuthn request.
  *
  * @param view Creates the WebView.
  * @param message The message sent from the client using injected JavaScript.
  * @param sourceOrigin The origin of the HTTPS request. Should not be null.
  * @param isMainFrame Should be set to true. Embedded frames are not
    supported.
  * @param replyProxy Passed in by JavaScript. Allows replying when wrapped in
    the Channel.
  * @return The message response.
  */
  @UiThread
  public void onPostMessage(
    @NonNull WebView view,
    @NonNull WebMessageCompat message,
    @NonNull Uri sourceOrigin,
    Boolean isMainFrame,
    @NonNull JavaScriptReplyProxy replyProxy,
  ) {
      if (messageData == null) {
        return;
    }
    onRequest(
      messageData,
      sourceOrigin,
      isMainFrame,
      JavaScriptReplyChannel(replyProxy)
    )
  }

  private void onRequest(
    String msg,
    Uri sourceOrigin,
    boolean isMainFrame,
    ReplyChannel reply
  ) {
      if (msg != null) {
        try {
          JSONObject jsonObj = new JSONObject(msg);
          String type = jsonObj.getString(TYPE_KEY);
          String message = jsonObj.getString(REQUEST_KEY);

          boolean isCreate = type.equals(CREATE_UNIQUE_KEY);
          boolean isGet = type.equals(GET_UNIQUE_KEY);

          if (havePendingRequest) {
              postErrorMessage(reply, "The request already in progress", type);
              return;
          }
          replyChannel = reply;
          if (!isMainFrame) {
              reportFailure("Requests from subframes are not supported", type);
              return;
          }
          String originScheme = sourceOrigin.getScheme();
          if (originScheme == null || !originScheme.toLowerCase().equals("https")) {
              reportFailure("WebAuthn not permitted for current URL", type);
              return;
          }

          // Verify that origin belongs to your website,
          // Requests of unknown origin may gain access to credential info.
          if (isUnknownOrigin(originScheme)) {
            return;
          }

          havePendingRequest = true;
          pendingRequestIsDoomed = false;

          // Use a temporary "replyCurrent" variable to send the data back,
          // while resetting the main "replyChannel" variable to null so it’s
          // ready for the next request.

          ReplyChannel replyCurrent = replyChannel;
          if (replyCurrent == null) {
              Log.i(TAG, "The reply channel was null, cannot continue");
              return;
          }

          if (isCreate) {
              handleCreateFlow(credentialManagerHandler, message, replyCurrent));
          } else if (isGet) {
              handleGetFlow(credentialManagerHandler, message, replyCurrent));
          } else {
              Log.i(TAG, "Incorrect request json");
          }
        } catch (JSONException e) {
        e.printStackTrace();
      }
    }
  }
}

对于handleCreateFlow和handleGetFlow，请参考GitHub 上的示例。

处理响应

要处理从原生应用发送到网页的响应，请在JavaScriptReplyChannel中添加JavaScriptReplyProxy。

Kotlin

class PasskeyWebListener(...)... {
// ...
  // The setup for the reply channel allows communication with JavaScript.
  private class JavaScriptReplyChannel(private val reply: JavaScriptReplyProxy) :
    ReplyChannel {
    override fun send(message: String?) {
      try {
        reply.postMessage(message!!)
      } catch (t: Throwable) {
        Log.i(TAG, "Reply failure due to: " + t.message);
      }
    }
  }

  // ReplyChannel is the interface where replies to the embedded site are
  // sent. This allows for testing since AndroidX bans mocking its objects.
  interface ReplyChannel {
    fun send(message: String?)
  }
}

Java

class PasskeyWebListener implements ... {
// ...

  // The setup for the reply channel allows communication with JavaScript.
  private static class JavaScriptReplyChannel implements ReplyChannel {
    private final JavaScriptReplyProxy reply;

    JavaScriptReplyChannel(JavaScriptReplyProxy reply) {
      this.reply = reply;
    }

    @Override
    public void send(String message) {
      reply.postMessage(message);
    }
  }

  // ReplyChannel is the interface where replies to the embedded site are
  // sent. This allows for testing since AndroidX bans mocking its objects.
  interface ReplyChannel {
    void send(String message);
  }
}

务必捕获原生应用中的任何错误并将其发送回 JavaScript 端。

与 WebView 集成

本节介绍如何设置 WebView 集成。

初始化 WebView

在您的 Android 应用的活动中，初始化一个WebView并设置一个配套的WebViewClient。WebViewClient处理与注入到WebView中的 JavaScript 代码的通信。

设置 WebView 并调用凭据管理器

Kotlin

val credentialManagerHandler = CredentialManagerHandler(this)
// ...

AndroidView(factory = {
  WebView(it).apply {
    settings.javaScriptEnabled = true

    // Test URL:
    val url = "https://credman-web-test.glitch.me/"
    val listenerSupported = WebViewFeature.isFeatureSupported(
      WebViewFeature.WEB_MESSAGE_LISTENER
    )
    if (listenerSupported) {
      // Inject local JavaScript that calls Credential Manager.
      hookWebAuthnWithListener(this, this@MainActivity,
      coroutineScope, credentialManagerHandler)
      } else {
        // Fallback routine for unsupported API levels.
      }
      loadUrl(url)
    }
  }
)

Java

// Example shown in the onCreate method of an Activity

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  WebView webView = findViewById(R.id.web_view);
  // Test URL:
  String url = "https://credman-web-test.glitch.me/";
  Boolean listenerSupported = WebViewFeature.isFeatureSupported(
    WebViewFeature.WEB_MESSAGE_LISTENER
  );
  if (listenerSupported) {
    // Inject local JavaScript that calls Credential Manager.
    hookWebAuthnWithListener(webView, this,
      coroutineScope, credentialManagerHandler)
  } else {
    // Fallback routine for unsupported API levels.
  }
  webView.loadUrl(url);
}

创建一个新的 WebView 客户端对象并将 JavaScript 注入网页

Kotlin

// This is an example call into hookWebAuthnWithListener
val passkeyWebListener = PasskeyWebListener(
  activity, coroutineScope, credentialManagerHandler
)

val webViewClient = object : WebViewClient() {
  override fun onPageStarted(view: WebView?, url: String?, favicon: Bitmap?) {
    super.onPageStarted(view, url, favicon)
    // Handle page load events
    passkeyWebListener.onPageStarted();
    webView.evaluateJavascript(PasskeyWebListener.INJECTED_VAL, null)
  }
}

webView.webViewClient = webViewClient

Java

// This is an example call into hookWebAuthnWithListener
PasskeyWebListener passkeyWebListener = new PasskeyWebListener(
  activity, credentialManagerHandler
)

WebViewClient webiewClient = new WebViewClient() {
  @Override
  public void onPageStarted(WebView view, String url, Bitmap favicon) {
    super.onPageStarted(view, url, favicon);
    // Handle page load events
    passkeyWebListener.onPageStarted();
    webView.evaulateJavascript(PasskeyWebListener.INJECTED_VAL, null);
  }
};

webView.setWebViewClient(webViewClient);

设置 Web 消息监听器

为了允许在 JavaScript 和 Android 应用之间发布消息，请使用WebViewCompat.addWebMessageListener方法设置 Web 消息监听器。

Kotlin

val rules = setOf("*")
if (WebViewFeature.isFeatureSupported(WebViewFeature.WEB_MESSAGE_LISTENER)) {
  WebViewCompat.addWebMessageListener(
    webView, PasskeyWebListener.INTERFACE_NAME, rules, passkeyWebListener
  )
}

Java

Set<String> rules = new HashSet<>(Arrays.asList("*"));

if (WebViewFeature.isFeatureSupported(WebViewFeature.WEB_MESSAGE_LISTENER)) {
  WebViewCompat.addWebMessageListener(
    webView, PasskeyWebListener.INTERFACE_NAME, rules, passkeyWebListener
  )
}

Web 集成

要了解如何构建 Web 集成，请查看创建用于无密码登录的密钥和通过表单自动填充使用密钥登录。

测试和部署

在受控环境中彻底测试整个流程，以确保 Android 应用、网页和后端之间的正确通信。

将集成解决方案部署到生产环境，确保后端可以处理传入的注册和身份验证请求。后端代码应为注册（创建）和身份验证（获取）过程生成初始 JSON。它还应处理从网页接收到的响应的验证和验证。

验证实现是否符合UX 建议。

重要说明

  • 使用提供的 JavaScript 代码来处理navigator.credentials.create()和navigator.credentials.get()操作。
  • PasskeyWebListener类是 Android 应用和 WebView 中 JavaScript 代码之间的桥梁。它处理消息传递、通信和所需操作的执行。
  • 调整提供的代码片段以适应项目的结构、命名约定和您可能拥有的任何特定要求。
  • 捕获原生应用端的错误并将其发送回 JavaScript 端。

通过遵循本指南并将凭据管理器 API 集成到使用 WebView 的 Android 应用中，您可以为用户提供安全且无缝的启用密钥的登录体验，同时有效地管理其凭据。