Use NoCredentials in case the emulator host is being connected to

docs/modules/ROOT/pages/pubsub.adoc

@@ -58,6 +58,10 @@ you need to set it instead of relying on the `quarkus.google.cloud.service-accou
 Another solution, is to inject a `CredentialsProvider` provided by the extension, and to use it inside the various PubSub
 builders and settings objects when, instantiating PubSub components.
 
+In case you are connecting to the emulator (and thus `quarkus.google.cloud.pubsub.emulator-host` is set), the
+extension will automatically use the `NoCredentialsProvider` for authentication. This behaviour can be disabled
+by setting the `quarkus.google.cloud.pubsub.use-emulator-credentials` to `false`.
+
 == Some example
 
 This is an example usage of the extension: we create a REST resource with a single endpoint that sends a message to the `test-topic` topic when hit.

pubsub/runtime/src/main/java/io/quarkiverse/googlecloudservices/pubsub/PubSubConfiguration.java

@@ -5,6 +5,7 @@
 import io.quarkus.runtime.annotations.ConfigPhase;
 import io.quarkus.runtime.annotations.ConfigRoot;
 import io.smallrye.config.ConfigMapping;
+import io.smallrye.config.WithDefault;
 
 @ConfigMapping(prefix = "quarkus.google.cloud.pubsub")
 @ConfigRoot(phase = ConfigPhase.RUN_TIME)
@@ -14,4 +15,14 @@ public interface PubSubConfiguration {
      */
     Optional<String> emulatorHost();
 
+    /**
+     * Forces the usage of emulator credentials. The logic automatically uses emulator credentials in case
+     * the emulatorHost is set.
+     * <ul>
+     * <li>If true: force usage of emulator credentials</li>
+     * <li>If false: force not using emulator credentials</li>
+     * </ul>
+     */
+    @WithDefault("true")
+    boolean useEmulatorCredentials();
 }

pubsub/runtime/src/main/java/io/quarkiverse/googlecloudservices/pubsub/QuarkusPubSub.java

@@ -4,9 +4,11 @@
 import java.util.Optional;
 import java.util.stream.StreamSupport;
 
+import com.google.api.gax.core.NoCredentialsProvider;
 import jakarta.annotation.PostConstruct;
 import jakarta.annotation.PreDestroy;
 import jakarta.enterprise.context.ApplicationScoped;
+import jakarta.enterprise.inject.Instance;
 import jakarta.inject.Inject;
 
 import com.google.api.gax.core.CredentialsProvider;
@@ -23,7 +25,7 @@
 @ApplicationScoped
 public class QuarkusPubSub {
     @Inject
-    CredentialsProvider credentialsProvider;
+    Instance<CredentialsProvider> credentialsProvider;
 
     @Inject
     GcpConfigHolder gcpConfigHolder;
@@ -64,7 +66,7 @@ public Subscriber subscriber(String subscription, MessageReceiver receiver) {
     public Subscriber subscriber(String subscription, String projectId, MessageReceiver receiver) {
         ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(projectId, subscription);
         var builder = Subscriber.newBuilder(subscriptionName, receiver)
-                .setCredentialsProvider(credentialsProvider);
+                .setCredentialsProvider(credentialsProvider());
         channelProvider.ifPresent(builder::setChannelProvider);
         return builder.build();
 
@@ -83,7 +85,7 @@ public Publisher publisher(String topic) throws IOException {
     public Publisher publisher(String topic, String projectId) throws IOException {
         TopicName topicName = TopicName.of(projectId, topic);
         var builder = Publisher.newBuilder(topicName)
-                .setCredentialsProvider(credentialsProvider);
+                .setCredentialsProvider(credentialsProvider());
         channelProvider.ifPresent(builder::setChannelProvider);
         return builder.build();
     }
@@ -93,7 +95,7 @@ public Publisher publisher(String topic, String projectId) throws IOException {
      */
     public SubscriptionAdminSettings subscriptionAdminSettings() throws IOException {
         var builder = SubscriptionAdminSettings.newBuilder()
-                .setCredentialsProvider(credentialsProvider);
+                .setCredentialsProvider(credentialsProvider());
         channelProvider.ifPresent(builder::setTransportChannelProvider);
         return builder.build();
     }
@@ -103,7 +105,7 @@ public SubscriptionAdminSettings subscriptionAdminSettings() throws IOException
      */
     public TopicAdminSettings topicAdminSettings() throws IOException {
         var builder = TopicAdminSettings.newBuilder()
-                .setCredentialsProvider(credentialsProvider);
+                .setCredentialsProvider(credentialsProvider());
         channelProvider.ifPresent(builder::setTransportChannelProvider);
         return builder.build();
     }
@@ -146,4 +148,12 @@ public Subscription createSubscription(String topic, String subscription) throws
                     PushConfig.getDefaultInstance(), 0));
         }
     }
+
+    private CredentialsProvider credentialsProvider() {
+        if (pubSubConfiguration.emulatorHost().isPresent() && pubSubConfiguration.useEmulatorCredentials()) {
+            return new NoCredentialsProvider();
+        } else {
+            return credentialsProvider.get();
+        }
+    }
 }