Add GCP auth extension module to contrib repo

Author: psx95

gcp-auth-extension/README.md

@@ -0,0 +1,68 @@
+# Google Cloud Authentication Extension for OpenTelemetry Java Agent
+
+The Google Cloud Auth Extension allows the users to export telemetry from their applications auto-instrumented using the OpenTelemetry Java Agent to Google Cloud using the built-in OTLP exporters.
+The extension takes care of the necessary configuration required to authenticate to GCP to successfully export telemetry.
+
+## Prerequisites
+
+### Ensure the presence of Google Cloud Credentials on your machine/environment
+
+```shell
+gcloud auth application-default login
+```
+Executing this command will save your application credentials to default path which will depend on the type of machine -
+- Linux, macOS: `$HOME/.config/gcloud/application_default_credentials.json`
+- Windows: `%APPDATA%\gcloud\application_default_credentials.json`
+
+**NOTE: This method of authentication is not recommended for production environments.**
+
+Next, export the credentials to `GOOGLE_APPLICATION_CREDENTIALS` environment variable -
+
+For Linux & MacOS:
+```shell
+export GOOGLE_APPLICATION_CREDENTIALS=$HOME/.config/gcloud/application_default_credentials.json
+```
+
+These credentials are built-in running in a Google App Engine, Google Cloud Shell or Google Compute Engine environment.
+
+### Configuring the extension
+
+The extension can be configured either by environment variables or system properties.
+
+Here is a list of configurable options for the extension:
+
+- `GOOGLE_CLOUD_PROJECT`: Environment variable that represents the Google Cloud Project ID to which the telemetry needs to be exported.
+  - Can also be configured using `google.cloud.project` system property.
+  - If this option is not configured, the extension would infer GCP Project ID from the application default credentials. For more information on application default credentials, see [here](https://cloud.google.com/docs/authentication/application-default-credentials).
+
+## Usage
+
+The OpenTelemetry Java Agent Extension can be easily added to any Java application by modifying the startup command to the application.
+For more information on Extensions, see the [documentation here](https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/examples/extension/README.md).
+
+Below is a snippet showing how to add the extension to a Java application using the Gradle build system.
+
+```gradle
+// Specify OpenTelemetry Autoinstrumentation Java Agent Path.
+def otelAgentPath = <OpenTelemetry Java Agent location>
+// Specify the path for Google Cloud Authentication Extension for the Java Agent.
+def extensionPath = <Google Cloud Authentication Extension location>
+def googleCloudProjectId = <Your Google Cloud Project ID>
+def googleOtlpEndpoint = <Google Cloud OTLP endpoint>
+
+application {
+   ...
+  "-javaagent:${otelAgentPath}",
+  "-Dotel.javaagent.extensions=${extensionPath}",
+  // Configure the GCP Auth extension using system properties.
+  // This can also be configured using environment variables.
+  "-Dgoogle.cloud.project=${googleCloudProjectId}",
+  // Configure auto instrumentation.
+  "-Dotel.exporter.otlp.traces.endpoint=${googleOtlpEndpoint}",
+  '-Dotel.java.global-autoconfigure.enabled=true',
+  // Optionally enable the built-in GCP resource detector
+  '-Dotel.resource.providers.gcp.enabled=true'
+  '-Dotel.traces.exporter=otlp',
+  '-Dotel.metrics.exporter=logging',
+}
+```

gcp-auth-extension/build.gradle.kts

@@ -0,0 +1,17 @@
+plugins {
+  id("otel.java-conventions")
+
+  id("otel.publish-conventions")
+}
+
+description = "OpenTelemetry Java Agent Extension that enables authentication support for OTLP exporters"
+otelJava.moduleName.set("io.opentelemetry.contrib.gcp.auth")
+
+dependencies {
+  testImplementation("org.junit.jupiter:junit-jupiter")
+  testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
+}
+
+tasks.test {
+  useJUnitPlatform()
+}

gcp-auth-extension/gradle.properties

@@ -0,0 +1,2 @@
+# TODO: uncomment when ready to mark as stable
+# otel.stable=true

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

@@ -0,0 +1,12 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.gcp.auth;
+
+public final class Main {
+  public void foo() {
+    // TODO: Implement this
+  }
+}

settings.gradle.kts

@@ -62,3 +62,4 @@ include(":gcp-resources")
 include(":span-stacktrace")
 include(":inferred-spans")
 include(":opamp-client")
+include(":gcp-auth-extension")