Add warning logs to indicate possible misconfiguration

Author: psx95

gcp-auth-extension/src/main/java/io/opentelemetry/contrib/gcp/auth/ConfigurableOption.java

@@ -51,7 +51,7 @@ enum ConfigurableOption {
    * configured using the environment variable `GOOGLE_OTEL_AUTH_TARGET_SIGNALS` or the system
    * property `google.otel.auth.target.signals`.
    */
-  GOOGLE_OTEL_AUTH_TARGET_SIGNALS("Target Signals for Google Auth Extension");
+  GOOGLE_OTEL_AUTH_TARGET_SIGNALS("Target Signals for Google Authentication Extension");
 
   private final String userReadableName;
   private final String environmentVariableName;
@@ -82,6 +82,15 @@ String getSystemProperty() {
     return this.systemPropertyName;
   }
 
+  /**
+   * Returns the user readable name associated with this option.
+   *
+   * @return the user readable name (e.g., "Google Cloud Quota Project ID")
+   */
+  String getUserReadableName() {
+    return this.userReadableName;
+  }
+
   /**
    * Retrieves the configured value for this option. This method checks the environment variable
    * first and then the system property.

gcp-auth-extension/src/main/java/io/opentelemetry/contrib/gcp/auth/GcpAuthAutoConfigurationCustomizerProvider.java

@@ -30,6 +30,8 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 import java.util.stream.Collectors;
 import javax.annotation.Nonnull;
 
@@ -50,6 +52,18 @@
 public class GcpAuthAutoConfigurationCustomizerProvider
     implements AutoConfigurationCustomizerProvider {
 
+  private static final Logger logger =
+      Logger.getLogger(GcpAuthAutoConfigurationCustomizerProvider.class.getName());
+  private static final String SIGNAL_TARGET_WARNING_FIX_SUGGESTION =
+      String.format(
+          "You may safely ignore this warning if it is intentional, otherwise please configure the '%s' by exporting valid values to environment variable: %s or by setting valid values in system property: %s.",
+          ConfigurableOption.GOOGLE_OTEL_AUTH_TARGET_SIGNALS.getUserReadableName(),
+          ConfigurableOption.GOOGLE_OTEL_AUTH_TARGET_SIGNALS.getEnvironmentVariable(),
+          ConfigurableOption.GOOGLE_OTEL_AUTH_TARGET_SIGNALS.getSystemProperty());
+  private static final String SIGNAL_TARGET_WARNING_MSG =
+      "GCP Authentication Extension is not configured for signal type: %s. "
+          + SIGNAL_TARGET_WARNING_FIX_SUGGESTION;
+
   static final String QUOTA_USER_PROJECT_HEADER = "x-goog-user-project";
   static final String GCP_USER_PROJECT_ID_KEY = "gcp.project_id";
 
@@ -110,6 +124,8 @@ private static SpanExporter customizeSpanExporter(
       SpanExporter exporter, GoogleCredentials credentials, ConfigProperties configProperties) {
     if (isSignalTargeted(SIGNAL_TYPE_TRACES, configProperties)) {
       return addAuthorizationHeaders(exporter, credentials, configProperties);
+    } else {
+      logger.log(Level.WARNING, String.format(SIGNAL_TARGET_WARNING_MSG, SIGNAL_TYPE_TRACES));
     }
     return exporter;
   }
@@ -118,6 +134,8 @@ private static MetricExporter customizeMetricExporter(
       MetricExporter exporter, GoogleCredentials credentials, ConfigProperties configProperties) {
     if (isSignalTargeted(SIGNAL_TYPE_METRICS, configProperties)) {
       return addAuthorizationHeaders(exporter, credentials, configProperties);
+    } else {
+      logger.log(Level.WARNING, String.format(SIGNAL_TARGET_WARNING_MSG, SIGNAL_TYPE_METRICS));
     }
     return exporter;
   }