feat(appcheck): Implement reCAPTCHA Enterprise App Check provider

appcheck/firebase-appcheck-recaptchaenterprise/api.txt

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+// Signature format: 3.0
+package com.google.firebase.appcheck.recaptchaenterprise {
+
+  public class RecaptchaEnterpriseAppCheckProviderFactory implements com.google.firebase.appcheck.AppCheckProviderFactory {
+    method public com.google.firebase.appcheck.AppCheckProvider create(com.google.firebase.FirebaseApp);
+    method public static com.google.firebase.appcheck.recaptchaenterprise.RecaptchaEnterpriseAppCheckProviderFactory getInstance(String);
+  }
+
+}
+

appcheck/firebase-appcheck-recaptchaenterprise/firebase-appcheck-recaptchaenterprise.gradle

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+plugins {
+    id 'firebase-library'
+}
+
+firebaseLibrary {
+    libraryGroup = "appcheck"
+    releaseNotes {
+        name.set("{{app_check}} Recaptcha Enterprise")
+        versionName.set("appcheck-recaptchaenterprise")
+    }
+}
+
+android {
+    adbOptions {
+        timeOutInMs 60 * 1000
+    }
+
+    namespace "com.google.firebase.appcheck.recaptchaenterprise"
+    compileSdkVersion project.compileSdkVersion
+    defaultConfig {
+        targetSdkVersion project.targetSdkVersion
+        minSdkVersion project.minSdkVersion
+        versionName version
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+    }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    testOptions.unitTests.includeAndroidResources = false
+}
+
+dependencies {
+    javadocClasspath libs.autovalue.annotations
+
+    api project(':appcheck:firebase-appcheck')
+    api libs.firebase.annotations
+    api libs.firebase.common.v2200
+    api libs.firebase.common.ktx
+    api libs.firebase.components.v1800
+    api libs.recaptcha.v1871
+
+    testImplementation(project(":integ-testing")) {
+        exclude group: 'com.google.firebase', module: 'firebase-common'
+        exclude group: 'com.google.firebase', module: 'firebase-components'
+    }
+    testImplementation libs.androidx.test.core
+    testImplementation libs.truth
+    testImplementation libs.junit
+    testImplementation libs.mockito.core.v5120
+    testImplementation libs.robolectric
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <application>
+        <service
+            android:name="com.google.firebase.components.ComponentDiscoveryService"
+            android:exported="false">
+            <meta-data
+                android:name="com.google.firebase.components:com.google.firebase.appcheck.recaptchaenterprise.FirebaseAppCheckRecaptchaEnterpriseRegistrar"
+                android:value="com.google.firebase.components.ComponentRegistrar" />
+        </service>
+    </application>
+</manifest>

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/FirebaseAppCheckRecaptchaEnterpriseRegistrar.java

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+package com.google.firebase.appcheck.recaptchaenterprise;
+
+import android.app.Application;
+import android.content.Context;
+import com.google.android.gms.common.annotation.KeepForSdk;
+import com.google.firebase.annotations.concurrent.Blocking;
+import com.google.firebase.annotations.concurrent.Lightweight;
+import com.google.firebase.appcheck.recaptchaenterprise.internal.FirebaseExecutors;
+import com.google.firebase.components.Component;
+import com.google.firebase.components.ComponentRegistrar;
+import com.google.firebase.components.Dependency;
+import com.google.firebase.components.Qualified;
+import com.google.firebase.platforminfo.LibraryVersionComponent;
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.Executor;
+
+/**
+ * {@link ComponentRegistrar} for setting up FirebaseAppCheck reCAPTCHA Enterprise's dependency
+ * injections in Firebase Android Components.
+ *
+ * @hide
+ */
+@KeepForSdk
+public class FirebaseAppCheckRecaptchaEnterpriseRegistrar implements ComponentRegistrar {
+  private static final String LIBRARY_NAME = "fire-app-check-recaptcha-enterprise";
+
+  @Override
+  public List<Component<?>> getComponents() {
+    Qualified<Executor> liteExecutor = Qualified.qualified(Lightweight.class, Executor.class);
+    Qualified<Executor> blockingExecutor = Qualified.qualified(Blocking.class, Executor.class);
+
+    return Arrays.asList(
+        Component.builder(Application.class)
+            .name(LIBRARY_NAME)
+            .add(Dependency.required(Context.class))
+            .factory(
+                container -> {
+                  Context context = container.get(Context.class);
+                  return (Application) context.getApplicationContext();
+                })
+            .build(),
+        Component.builder(FirebaseExecutors.class)
+            .name(LIBRARY_NAME)
+            .add(Dependency.required(liteExecutor))
+            .add(Dependency.required(blockingExecutor))
+            .factory(
+                container ->
+                    new FirebaseExecutors(
+                        container.get(liteExecutor), container.get(blockingExecutor)))
+            .build(),
+        LibraryVersionComponent.create(LIBRARY_NAME, BuildConfig.VERSION_NAME));
+  }
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/RecaptchaEnterpriseAppCheckProviderFactory.java

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+package com.google.firebase.appcheck.recaptchaenterprise;
+
+import android.app.Application;
+import androidx.annotation.NonNull;
+import com.google.firebase.FirebaseApp;
+import com.google.firebase.appcheck.AppCheckProvider;
+import com.google.firebase.appcheck.AppCheckProviderFactory;
+import com.google.firebase.appcheck.FirebaseAppCheck;
+import com.google.firebase.appcheck.recaptchaenterprise.internal.FirebaseExecutors;
+import com.google.firebase.appcheck.recaptchaenterprise.internal.RecaptchaEnterpriseAppCheckProvider;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * Implementation of an {@link AppCheckProviderFactory} that builds <br>
+ * {@link RecaptchaEnterpriseAppCheckProvider}s. This is the default implementation.
+ */
+public class RecaptchaEnterpriseAppCheckProviderFactory implements AppCheckProviderFactory {
+
+  private static FirebaseExecutors firebaseExecutors;
+  private static final Map<String, RecaptchaEnterpriseAppCheckProviderFactory> factoryInstances =
+      new ConcurrentHashMap<>();
+  private final String siteKey;
+  private volatile RecaptchaEnterpriseAppCheckProvider provider;
+
+  private RecaptchaEnterpriseAppCheckProviderFactory(@NonNull String siteKey) {
+    this.siteKey = siteKey;
+  }
+
+  /** Gets an instance of this class for installation into a {@link FirebaseAppCheck} instance. */
+  @NonNull
+  public static RecaptchaEnterpriseAppCheckProviderFactory getInstance(@NonNull String siteKey) {
+    RecaptchaEnterpriseAppCheckProviderFactory factory = factoryInstances.get(siteKey);
+    if (factory == null) {
+      synchronized (factoryInstances) {
+        factory = factoryInstances.get(siteKey);
+        if (factory == null) {
+          factory = new RecaptchaEnterpriseAppCheckProviderFactory(siteKey);
+          factoryInstances.put(siteKey, factory);
+        }
+      }
+    }
+    return factory;
+  }
+
+  @NonNull
+  @Override
+  @SuppressWarnings("FirebaseUseExplicitDependencies")
+  public AppCheckProvider create(@NonNull FirebaseApp firebaseApp) {
+    if (provider == null) {
+      synchronized (this) {
+        if (provider == null) {
+          if (RecaptchaEnterpriseAppCheckProviderFactory.firebaseExecutors == null) {
+            firebaseExecutors = firebaseApp.get(FirebaseExecutors.class);
+          }
+          Application application = firebaseApp.get(Application.class);
+
+          provider =
+              new RecaptchaEnterpriseAppCheckProvider(
+                  firebaseApp,
+                  application,
+                  siteKey,
+                  firebaseExecutors.getLiteExecutor(),
+                  firebaseExecutors.getBlockingExecutor());
+        }
+      }
+    }
+    return provider;
+  }
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/internal/ExchangeRecaptchaEnterpriseTokenRequest.java

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+package com.google.firebase.appcheck.recaptchaenterprise.internal;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+/**
+ * Client-side model of the ExchangeRecaptchaEnterpriseTokenRequest payload from the Firebase App
+ * Check Token Exchange API.
+ */
+public class ExchangeRecaptchaEnterpriseTokenRequest {
+
+  @VisibleForTesting
+  static final String RECAPTCHA_ENTERPRISE_TOKEN_KEY = "recaptchaEnterpriseToken";
+
+  private final String recaptchaEnterpriseToken;
+
+  public ExchangeRecaptchaEnterpriseTokenRequest(@NonNull String recaptchaEnterpriseToken) {
+    this.recaptchaEnterpriseToken = recaptchaEnterpriseToken;
+  }
+
+  @NonNull
+  public String toJsonString() throws JSONException {
+    JSONObject jsonObject = new JSONObject();
+    jsonObject.put(RECAPTCHA_ENTERPRISE_TOKEN_KEY, recaptchaEnterpriseToken);
+
+    return jsonObject.toString();
+  }
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/internal/FirebaseExecutors.java

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+package com.google.firebase.appcheck.recaptchaenterprise.internal;
+
+import com.google.firebase.annotations.concurrent.Blocking;
+import com.google.firebase.annotations.concurrent.Lightweight;
+import java.util.concurrent.Executor;
+
+/**
+ * This class encapsulates a {@link com.google.firebase.annotations.concurrent.Lightweight} executor
+ * and a {@link com.google.firebase.annotations.concurrent.Blocking} executor, making them available
+ * for various asynchronous operations related to reCAPTCHA Enterprise App Check.
+ */
+public class FirebaseExecutors {
+  private final Executor liteExecutor;
+  private final Executor blockingExecutor;
+
+  public FirebaseExecutors(
+      @Lightweight Executor liteExecutor, @Blocking Executor blockingExecutor) {
+    this.liteExecutor = liteExecutor;
+    this.blockingExecutor = blockingExecutor;
+  }
+
+  public Executor getLiteExecutor() {
+    return liteExecutor;
+  }
+
+  public Executor getBlockingExecutor() {
+    return blockingExecutor;
+  }
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/internal/RecaptchaEnterpriseAppCheckProvider.java

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+package com.google.firebase.appcheck.recaptchaenterprise.internal;
+
+import android.app.Application;
+import android.util.Log;
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+import com.google.android.gms.tasks.Task;
+import com.google.android.gms.tasks.Tasks;
+import com.google.android.recaptcha.Recaptcha;
+import com.google.android.recaptcha.RecaptchaAction;
+import com.google.android.recaptcha.RecaptchaTasksClient;
+import com.google.firebase.FirebaseApp;
+import com.google.firebase.annotations.concurrent.Blocking;
+import com.google.firebase.annotations.concurrent.Lightweight;
+import com.google.firebase.appcheck.AppCheckProvider;
+import com.google.firebase.appcheck.AppCheckToken;
+import com.google.firebase.appcheck.internal.DefaultAppCheckToken;
+import com.google.firebase.appcheck.internal.NetworkClient;
+import com.google.firebase.appcheck.internal.RetryManager;
+import java.nio.charset.StandardCharsets;
+import java.util.Objects;
+import java.util.concurrent.Executor;
+
+public class RecaptchaEnterpriseAppCheckProvider implements AppCheckProvider {
+
+  private final RecaptchaAction recaptchaAction = RecaptchaAction.custom("fire_app_check");
+  private final Task<RecaptchaTasksClient> recaptchaTasksClientTask;
+  private final Executor liteExecutor;
+  private final Executor blockingExecutor;
+  private final RetryManager retryManager;
+  private final NetworkClient networkClient;
+  private static final String TAG = "rCEAppCheckProvider";
+
+  public RecaptchaEnterpriseAppCheckProvider(
+      @NonNull FirebaseApp firebaseApp,
+      @NonNull Application application,
+      @NonNull String siteKey,
+      @Lightweight Executor liteExecutor,
+      @Blocking Executor blockingExecutor) {
+    this.liteExecutor = liteExecutor;
+    this.blockingExecutor = blockingExecutor;
+    this.retryManager = new RetryManager();
+    this.networkClient = new NetworkClient(firebaseApp);
+    recaptchaTasksClientTask = Recaptcha.fetchTaskClient(application, siteKey);
+  }
+
+  @VisibleForTesting
+  RecaptchaEnterpriseAppCheckProvider(
+      @Lightweight Executor liteExecutor,
+      @Blocking Executor blockingExecutor,
+      @NonNull RetryManager retryManager,
+      @NonNull NetworkClient networkClient,
+      @NonNull RecaptchaTasksClient recaptchaTasksClient) {
+    this.liteExecutor = liteExecutor;
+    this.blockingExecutor = blockingExecutor;
+    this.retryManager = retryManager;
+    this.networkClient = networkClient;
+    this.recaptchaTasksClientTask = Tasks.forResult(recaptchaTasksClient);
+  }
+
+  @NonNull
+  @Override
+  public Task<AppCheckToken> getToken() {
+    return getRecaptchaEnterpriseAttestation()
+        .onSuccessTask(
+            liteExecutor,
+            recaptchaEnterpriseToken -> {
+              ExchangeRecaptchaEnterpriseTokenRequest request =
+                  new ExchangeRecaptchaEnterpriseTokenRequest(recaptchaEnterpriseToken);
+              return Tasks.call(
+                  blockingExecutor,
+                  () ->
+                      networkClient.exchangeAttestationForAppCheckToken(
+                          request.toJsonString().getBytes(StandardCharsets.UTF_8),
+                          NetworkClient.RECAPTCHA_ENTERPRISE,
+                          retryManager));
+            })
+        .onSuccessTask(
+            liteExecutor,
+            appCheckTokenResponse ->
+                Tasks.forResult(
+                    DefaultAppCheckToken.constructFromAppCheckTokenResponse(
+                        appCheckTokenResponse)));
+  }
+
+  @NonNull
+  private Task<String> getRecaptchaEnterpriseAttestation() {
+    return recaptchaTasksClientTask.continueWithTask(
+        blockingExecutor,
+        task -> {
+          if (task.isSuccessful()) {
+            RecaptchaTasksClient client = task.getResult();
+            return client.executeTask(recaptchaAction);
+          } else {
+            Log.w(TAG, "Recaptcha task failed", task.getException());
+            throw Objects.requireNonNull(task.getException());
+          }
+        });
+  }
+}

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/internal/package-info.java

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+/** @hide */
+package com.google.firebase.appcheck.recaptchaenterprise.internal;