enable ALTS bound token (for DirectPath) in the grpc channel provider

Author: rockspore

google-cloud-storage/src/main/java/com/google/cloud/storage/GrpcStorageOptions.java

@@ -50,6 +50,7 @@
 import com.google.api.gax.tracing.ApiTracerFactory;
 import com.google.api.pathtemplate.PathTemplate;
 import com.google.auth.Credentials;
+import com.google.auth.oauth2.ComputeEngineCredentials;
 import com.google.cloud.NoCredentials;
 import com.google.cloud.ServiceFactory;
 import com.google.cloud.ServiceOptions;
@@ -318,7 +319,8 @@ private Tuple<StorageSettings, Opts<UserProject>> resolveSettingsAndOpts() throw
         InstantiatingGrpcChannelProvider.newBuilder()
             .setEndpoint(endpoint)
             .setAllowNonDefaultServiceAccount(true)
-            .setAttemptDirectPath(attemptDirectPath);
+            .setAttemptDirectPath(attemptDirectPath)
+            .setAllowHardBoundTokenTypes(Arrays.asList(InstantiatingGrpcChannelProvider.HardBoundTokenTypes.ALTS));
 
     if (!NoopGrpcInterceptorProvider.INSTANCE.equals(grpcInterceptorProvider)) {
       channelProviderBuilder.setInterceptorProvider(grpcInterceptorProvider);