Implement 3P GetAppCheckToken API.

Author: rosalyntan

appcheck/firebase-appcheck/src/main/java/com/google/firebase/appcheck/FirebaseAppCheck.java

@@ -16,6 +16,7 @@
 
 import android.annotation.SuppressLint;
 import androidx.annotation.NonNull;
+import com.google.android.gms.tasks.Task;
 import com.google.firebase.FirebaseApp;
 import com.google.firebase.appcheck.interop.AppCheckTokenListener;
 import com.google.firebase.appcheck.interop.InternalAppCheckTokenProvider;
@@ -69,4 +70,30 @@ public abstract void installAppCheckProviderFactory(
 
   /** Sets the {@code isTokenAutoRefreshEnabled} flag. */
   public abstract void setTokenAutoRefreshEnabled(boolean isTokenAutoRefreshEnabled);
+
+  /**
+   * Requests a Firebase App Check token. This method should be used ONLY if you need to authorize
+   * requests to a non-Firebase backend. Requests to Firebase backends are authorized automatically
+   * if configured.
+   */
+  @NonNull
+  public abstract Task<AppCheckToken> getAppCheckToken(boolean forceRefresh);
+
+  /**
+   * Registers an {@link AppCheckListener} to changes in the token state. This method should be used
+   * ONLY if you need to authorize requests to a non-Firebase backend. Requests to Firebase backends
+   * are authorized automatically if configured.
+   */
+  public abstract void addAppCheckListener(@NonNull AppCheckListener listener);
+
+  /** Unregisters an {@link AppCheckListener} to changes in the token state. */
+  public abstract void removeAppCheckListener(@NonNull AppCheckListener listener);
+
+  public interface AppCheckListener {
+    /**
+     * This method gets invoked on the UI thread on changes to the token state. Does not trigger on
+     * token expiry.
+     */
+    void onAppCheckTokenChanged(@NonNull AppCheckToken token);
+  }
 }

appcheck/firebase-appcheck/src/main/java/com/google/firebase/appcheck/internal/DefaultFirebaseAppCheck.java

@@ -46,6 +46,7 @@ public class DefaultFirebaseAppCheck extends FirebaseAppCheck {
   private final Provider<UserAgentPublisher> userAgentPublisherProvider;
   private final Provider<HeartBeatInfo> heartBeatInfoProvider;
   private final List<AppCheckTokenListener> appCheckTokenListenerList;
+  private final List<AppCheckListener> appCheckListenerList;
   private final StorageHelper storageHelper;
   private final TokenRefreshManager tokenRefreshManager;
   private final Clock clock;
@@ -65,6 +66,7 @@ public DefaultFirebaseAppCheck(
     this.userAgentPublisherProvider = userAgentPublisherProvider;
     this.heartBeatInfoProvider = heartBeatInfoProvider;
     this.appCheckTokenListenerList = new ArrayList<>();
+    this.appCheckListenerList = new ArrayList<>();
     this.storageHelper =
         new StorageHelper(firebaseApp.getApplicationContext(), firebaseApp.getPersistenceKey());
     this.tokenRefreshManager =
@@ -110,7 +112,8 @@ public void resetAppCheckState() {
   public void addAppCheckTokenListener(@NonNull AppCheckTokenListener listener) {
     checkNotNull(listener);
     appCheckTokenListenerList.add(listener);
-    tokenRefreshManager.onListenerCountChanged(appCheckTokenListenerList.size());
+    tokenRefreshManager.onListenerCountChanged(
+        appCheckTokenListenerList.size() + appCheckListenerList.size());
     // If there is a token available, trigger the listener with the current token.
     if (hasValidToken()) {
       listener.onAppCheckTokenChanged(
@@ -122,7 +125,28 @@ public void addAppCheckTokenListener(@NonNull AppCheckTokenListener listener) {
   public void removeAppCheckTokenListener(@NonNull AppCheckTokenListener listener) {
     checkNotNull(listener);
     appCheckTokenListenerList.remove(listener);
-    tokenRefreshManager.onListenerCountChanged(appCheckTokenListenerList.size());
+    tokenRefreshManager.onListenerCountChanged(
+        appCheckTokenListenerList.size() + appCheckListenerList.size());
+  }
+
+  @Override
+  public void addAppCheckListener(@NonNull AppCheckListener listener) {
+    checkNotNull(listener);
+    appCheckListenerList.add(listener);
+    tokenRefreshManager.onListenerCountChanged(
+        appCheckTokenListenerList.size() + appCheckListenerList.size());
+    // If there is a token available, trigger the listener with the current token.
+    if (hasValidToken()) {
+      listener.onAppCheckTokenChanged(cachedToken);
+    }
+  }
+
+  @Override
+  public void removeAppCheckListener(@NonNull AppCheckListener listener) {
+    checkNotNull(listener);
+    appCheckListenerList.remove(listener);
+    tokenRefreshManager.onListenerCountChanged(
+        appCheckTokenListenerList.size() + appCheckListenerList.size());
   }
 
   @NonNull
@@ -137,22 +161,31 @@ public Task<AppCheckTokenResult> getToken(boolean forceRefresh) {
               new FirebaseException("No AppCheckProvider installed.")));
     }
     // TODO: Cache the in-flight task.
+    return fetchTokenResultFromProvider();
+  }
+
+  @NonNull
+  @Override
+  public Task<AppCheckToken> getAppCheckToken(boolean forceRefresh) {
+    if (!forceRefresh && hasValidToken()) {
+      return Tasks.forResult(cachedToken);
+    }
+    if (appCheckProvider == null) {
+      return Tasks.forException(new FirebaseException("No AppCheckProvider installed."));
+    }
     return fetchTokenFromProvider();
   }
 
   /** Fetches an {@link AppCheckTokenResult} via the installed {@link AppCheckProvider}. */
-  Task<AppCheckTokenResult> fetchTokenFromProvider() {
-    return appCheckProvider
-        .getToken()
+  Task<AppCheckTokenResult> fetchTokenResultFromProvider() {
+    return fetchTokenFromProvider()
         .continueWithTask(
             new Continuation<AppCheckToken, Task<AppCheckTokenResult>>() {
               @Override
               public Task<AppCheckTokenResult> then(@NonNull Task<AppCheckToken> task) {
                 if (task.isSuccessful()) {
-                  AppCheckToken token = task.getResult();
-                  updateStoredToken(token);
                   AppCheckTokenResult tokenResult =
-                      DefaultAppCheckTokenResult.constructFromAppCheckToken(token);
+                      DefaultAppCheckTokenResult.constructFromAppCheckToken(task.getResult());
                   for (AppCheckTokenListener listener : appCheckTokenListenerList) {
                     listener.onAppCheckTokenChanged(tokenResult);
                   }
@@ -168,6 +201,26 @@ public Task<AppCheckTokenResult> then(@NonNull Task<AppCheckToken> task) {
             });
   }
 
+  /** Fetches an {@link AppCheckToken} via the installed {@link AppCheckProvider}. */
+  Task<AppCheckToken> fetchTokenFromProvider() {
+    return appCheckProvider
+        .getToken()
+        .continueWithTask(
+            new Continuation<AppCheckToken, Task<AppCheckToken>>() {
+              @Override
+              public Task<AppCheckToken> then(@NonNull Task<AppCheckToken> task) {
+                if (task.isSuccessful()) {
+                  AppCheckToken token = task.getResult();
+                  updateStoredToken(token);
+                  for (AppCheckListener listener : appCheckListenerList) {
+                    listener.onAppCheckTokenChanged(token);
+                  }
+                }
+                return task;
+              }
+            });
+  }
+
   @Nullable
   String getUserAgent() {
     return userAgentPublisherProvider.get() != null