Add back AppEngineCredentials

README.md

@@ -96,9 +96,9 @@ There are multiple ways to authenticate to use Google Cloud services.
 `gcloud-java` looks for credentials in the following order, stopping once it finds credentials:
 
 1. Credentials supplied when building the service options
-2. Key file pointed to by the GOOGLE_APPLICATION_CREDENTIALS environment variable
-3. Google Cloud SDK credentials
-4. App Engine credentials
+2. App Engine credentials
+3. Key file pointed to by the GOOGLE_APPLICATION_CREDENTIALS environment variable
+4. Google Cloud SDK credentials
 5. Compute Engine credentials
 
 Google Cloud Datastore

gcloud-java-core/pom.xml

@@ -33,17 +33,6 @@
         </exclusion>
       </exclusions>
     </dependency>
-    <dependency>
-      <groupId>com.google.auth</groupId>
-      <artifactId>google-auth-library-appengine</artifactId>
-      <version>0.3.1</version>
-      <exclusions>
-        <exclusion>
-          <groupId>com.google.guava</groupId>
-          <artifactId>guava-jdk5</artifactId>
-        </exclusion>
-      </exclusions>
-    </dependency>
     <dependency>
       <groupId>com.google.http-client</groupId>
       <artifactId>google-http-client</artifactId>

gcloud-java-core/src/main/java/com/google/gcloud/AuthCredentials.java

@@ -19,6 +19,7 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
+import com.google.api.client.googleapis.extensions.appengine.auth.oauth2.AppIdentityCredential;
 import com.google.api.client.http.HttpRequestInitializer;
 import com.google.api.client.http.HttpTransport;
 import com.google.api.client.json.jackson.JacksonFactory;
@@ -38,6 +39,45 @@
  */
 public abstract class AuthCredentials implements Restorable<AuthCredentials> {
 
+  private static class AppEngineAuthCredentials extends AuthCredentials {
+
+    private static final AuthCredentials INSTANCE = new AppEngineAuthCredentials();
+    private static final AppEngineAuthCredentialsState STATE =
+        new AppEngineAuthCredentialsState();
+
+    private static class AppEngineAuthCredentialsState
+        implements RestorableState<AuthCredentials>, Serializable {
+
+      private static final long serialVersionUID = 3558563960848658928L;
+
+      @Override
+      public AuthCredentials restore() {
+        return INSTANCE;
+      }
+
+      @Override
+      public int hashCode() {
+        return getClass().getName().hashCode();
+      }
+
+      @Override
+      public boolean equals(Object obj) {
+        return obj instanceof AppEngineAuthCredentialsState;
+      }
+    }
+
+    @Override
+    protected HttpRequestInitializer httpRequestInitializer(HttpTransport transport,
+        Set<String> scopes) {
+      return new AppIdentityCredential(scopes);
+    }
+
+    @Override
+    public RestorableState<AuthCredentials> capture() {
+      return STATE;
+    }
+  }
+
   public static class ServiceAccountAuthCredentials extends AuthCredentials {
 
     private final String account;
@@ -181,12 +221,16 @@ public RestorableState<AuthCredentials> capture() {
   protected abstract HttpRequestInitializer httpRequestInitializer(HttpTransport transport,
       Set<String> scopes);
 
+  public static AuthCredentials createForAppEngine() {
+    return AppEngineAuthCredentials.INSTANCE;
+  }
+
   /**
    * Returns the Application Default Credentials.
    *
    * <p>Returns the Application Default Credentials which are credentials that identify and
    * authorize the whole application. This is the built-in service account if running on
-   * Google App/Compute Engine or the credentials file can be read from the path in the environment
+   * Google Compute Engine or the credentials file can be read from the path in the environment
    * variable GOOGLE_APPLICATION_CREDENTIALS.
    * </p>
    *

gcloud-java-core/src/main/java/com/google/gcloud/ServiceOptions.java

@@ -356,6 +356,15 @@ protected boolean projectIdRequired() {
   }
 
   private static AuthCredentials defaultAuthCredentials() {
+    // Consider App Engine.
+    if (appEngineAppId() != null) {
+      try {
+        return AuthCredentials.createForAppEngine();
+      } catch (Exception ignore) {
+        // Maybe not on App Engine
+      }
+    }
+
     try {
       return AuthCredentials.createApplicationDefaults();
     } catch (Exception ex) {

gcloud-java-datastore/src/test/java/com/google/gcloud/datastore/SerializationTest.java

@@ -134,6 +134,7 @@ public class SerializationTest {
   @Test
   public void testServiceOptions() throws Exception {
     DatastoreOptions options = DatastoreOptions.builder()
+        .authCredentials(AuthCredentials.createForAppEngine())
         .normalizeDataset(false)
         .projectId("ds1")
         .build();

gcloud-java-storage/src/test/java/com/google/gcloud/storage/SerializationTest.java

@@ -75,6 +75,7 @@ public class SerializationTest {
   public void testServiceOptions() throws Exception {
     StorageOptions options = StorageOptions.builder()
         .projectId("p1")
+        .authCredentials(AuthCredentials.createForAppEngine())
         .build();
     StorageOptions serializedCopy = serializeAndDeserialize(options);
     assertEquals(options, serializedCopy);