fix: add scope codes to the stub provider

Author: hannahrogers-google

google-cloud-pubsublite/src/main/java/com/google/cloud/pubsublite/Stubs.java

@@ -15,6 +15,7 @@
 package com.google.cloud.pubsublite;
 
 import com.google.auth.oauth2.GoogleCredentials;
+import com.google.common.collect.ImmutableList;
 import io.grpc.Channel;
 import io.grpc.ManagedChannelBuilder;
 import io.grpc.auth.MoreCallCredentials;
@@ -23,11 +24,17 @@
 import java.util.function.Function;
 
 public class Stubs {
+  private static final ImmutableList<String> DEFAULT_SERVICE_SCOPES =
+    ImmutableList.of("https://www.googleapis.com/auth/cloud-platform");
+
   public static <StubT extends AbstractStub<StubT>> StubT defaultStub(
       String target, Function<Channel, StubT> stubFactory) throws IOException {
     return stubFactory
         .apply(ManagedChannelBuilder.forTarget(target).build())
-        .withCallCredentials(MoreCallCredentials.from(GoogleCredentials.getApplicationDefault()));
+        .withCallCredentials(MoreCallCredentials.from(
+          GoogleCredentials
+            .getApplicationDefault()
+            .createScoped(DEFAULT_SERVICE_SCORES)));
   }
 
   private Stubs() {}