Add GCP authentication extension

gcp-auth-extension/README.md

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+# 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
+
+### With OpenTelemetry Java agent
+
+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>
+
+val autoconf_config = listOf(
+  "-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'
+)
+
+application {
+  ...
+  applicationDefaultJvmArgs = autoconf_config
+  ...
+}
+```
+
+### Without OpenTelemetry Java agent
+
+This extension can be used without the OpenTelemetry Java agent by leveraging the [OpenTelemetry SDK Autoconfigure](https://github.com/open-telemetry/opentelemetry-java/blob/main/sdk-extensions/autoconfigure/README.md) module.\
+When using the autoconfigured SDK, simply adding this extension as a dependency automatically configures authentication headers and resource attributes for spans, enabling export to Google Cloud.
+
+Below is a snippet showing how to use this extension as a dependency when the application is not instrumented using the OpenTelemetry Java agent.
+
+```gradle
+dependencies {
+    implementation("io.opentelemetry:opentelemetry-api")
+    implementation("io.opentelemetry:opentelemetry-sdk")
+    implementation("io.opentelemetry:opentelemetry-exporter-otlp")
+    implementation("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure")
+    // use the shaded variant of the dependency
+    implementation("io.opentelemetry.contrib:opentelemetry-gcp-auth-extension")
+
+    // other dependencies
+    ...
+
+}
+
+val autoconf_config = listOf(
+  '-Dgoogle.cloud.project=your-gcp-project-id',
+  '-Dotel.exporter.otlp.endpoint=https://your.otlp.endpoint:1234',
+  '-Dotel.traces.exporter=otlp',
+  '-Dotel.java.global-autoconfigure.enabled=true'
+
+  // any additional args
+  ...
+)
+
+application {
+  applicationDefaultJvmArgs = autoconf_config
+
+  // additional configuration
+  ...
+}
+```
+
+## Component Owners
+
+- [Josh Suereth](https://github.com/jsuereth), Google
+- [Pranav Sharma](https://github.com/psx95), Google
+
+Learn more about component owners in [component_owners.yml](../.github/component_owners.yml).

gcp-auth-extension/build.gradle.kts

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+plugins {
+  id("otel.java-conventions")
+  id("otel.publish-conventions")
+  id("com.github.johnrengelman.shadow")
+  id("org.springframework.boot") version "2.7.18"
+}
+
+description = "OpenTelemetry Java Agent Extension that enables authentication support for OTLP exporters"
+otelJava.moduleName.set("io.opentelemetry.contrib.gcp.auth")
+
+val agent: Configuration by configurations.creating {
+  isCanBeResolved = true
+  isCanBeConsumed = false
+}
+
+dependencies {
+  annotationProcessor("com.google.auto.service:auto-service")
+  // We use `compileOnly` dependency because during runtime all necessary classes are provided by
+  // javaagent itself.
+  compileOnly("com.google.auto.service:auto-service-annotations")
+  compileOnly("io.opentelemetry:opentelemetry-api")
+  compileOnly("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure")
+  compileOnly("io.opentelemetry:opentelemetry-exporter-otlp")
+
+  // Only dependencies added to `implementation` configuration will be picked up by Shadow plugin
+  implementation("com.google.auth:google-auth-library-oauth2-http:1.30.1")
+
+  // Test dependencies
+  testCompileOnly("com.google.auto.service:auto-service-annotations")
+  testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine")
+  testImplementation("org.junit.jupiter:junit-jupiter-api")
+
+  testImplementation("io.opentelemetry:opentelemetry-api")
+  testImplementation("io.opentelemetry:opentelemetry-exporter-otlp")
+  testImplementation("io.opentelemetry:opentelemetry-sdk-testing")
+  testImplementation("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure")
+  testImplementation("io.opentelemetry.instrumentation:opentelemetry-instrumentation-annotations")
+
+  testImplementation("org.awaitility:awaitility")
+  testImplementation("org.mockito:mockito-inline")
+  testImplementation("org.mockito:mockito-junit-jupiter")
+  testImplementation("org.mock-server:mockserver-netty:5.15.0")
+  testImplementation("io.opentelemetry.proto:opentelemetry-proto:1.4.0-alpha")
+  testImplementation("org.springframework.boot:spring-boot-starter-web:2.7.18")
+  testImplementation("org.springframework.boot:spring-boot-starter:2.7.18")
+  testImplementation("org.springframework.boot:spring-boot-starter-test:2.7.18")
+
+  agent("io.opentelemetry.javaagent:opentelemetry-javaagent")
+}
+
+tasks {
+  test {
+    useJUnitPlatform()
+    // exclude integration test
+    exclude("io/opentelemetry/contrib/gcp/auth/GcpAuthExtensionEndToEndTest.class")
+  }
+
+  shadowJar {
+    archiveClassifier.set("")
+  }
+
+  jar {
+    // Disable standard jar
+    enabled = false
+  }
+
+  assemble {
+    dependsOn(shadowJar)
+  }
+
+  bootJar {
+    // disable bootJar in build since it only runs as part of test
+    enabled = false
+  }
+}
+
+val builtLibsDir = layout.buildDirectory.dir("libs").get().asFile.absolutePath
+val javaAgentJarPath = "$builtLibsDir/otel-agent.jar"
+val authExtensionJarPath = "${tasks.shadowJar.get().archiveFile.get()}"
+
+tasks.register<Copy>("copyAgent") {
+  into(layout.buildDirectory.dir("libs"))
+  from(configurations.named("agent") {
+    rename("opentelemetry-javaagent(.*).jar", "otel-agent.jar")
+  })
+}
+
+tasks.register<Test>("IntegrationTest") {
+  dependsOn(tasks.shadowJar)
+  dependsOn(tasks.named("copyAgent"))
+
+  useJUnitPlatform()
+  // include only the integration test file
+  include("io/opentelemetry/contrib/gcp/auth/GcpAuthExtensionEndToEndTest.class")
+
+  val fakeCredsFilePath = project.file("src/test/resources/fakecreds.json").absolutePath
+
+  environment("GOOGLE_CLOUD_QUOTA_PROJECT", "quota-project-id")
+  environment("GOOGLE_APPLICATION_CREDENTIALS", fakeCredsFilePath)
+  jvmArgs = listOf(
+    "-javaagent:$javaAgentJarPath",
+    "-Dotel.javaagent.extensions=$authExtensionJarPath",
+    "-Dgoogle.cloud.project=my-gcp-project",
+    "-Dotel.java.global-autoconfigure.enabled=true",
+    "-Dotel.exporter.otlp.endpoint=http://localhost:4318",
+    "-Dotel.resource.providers.gcp.enabled=true",
+    "-Dotel.traces.exporter=otlp",
+    "-Dotel.bsp.schedule.delay=2000",
+    "-Dotel.metrics.exporter=none",
+    "-Dotel.logs.exporter=none",
+    "-Dotel.exporter.otlp.protocol=http/protobuf",
+    "-Dmockserver.logLevel=off"
+  )
+}

gcp-auth-extension/gradle.properties

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+# TODO: uncomment when ready to mark as stable
+# otel.stable=true

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

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.gcp.auth;
+
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigurationException;
+import java.util.Locale;
+import java.util.function.Supplier;
+
+/**
+ * An enum representing configurable options for a GCP Authentication Extension. Each option has a
+ * user-readable name and can be configured using environment variables or system properties.
+ */
+public enum ConfigurableOption {
+  /**
+   * Represents the Google Cloud Project ID option. Can be configured using the environment variable
+   * `GOOGLE_CLOUD_PROJECT` or the system property `google.cloud.project`.
+   */
+  GOOGLE_CLOUD_PROJECT("Google Cloud Project ID");
+
+  private final String userReadableName;
+  private final String environmentVariableName;
+  private final String systemPropertyName;
+
+  ConfigurableOption(String userReadableName) {
+    this.userReadableName = userReadableName;
+    this.environmentVariableName = this.name();
+    this.systemPropertyName =
+        this.environmentVariableName.toLowerCase(Locale.ENGLISH).replace('_', '.');
+  }
+
+  /**
+   * Returns the environment variable name associated with this option.
+   *
+   * @return the environment variable name (e.g., GOOGLE_CLOUD_PROJECT)
+   */
+  String getEnvironmentVariable() {
+    return this.environmentVariableName;
+  }
+
+  /**
+   * Returns the system property name associated with this option.
+   *
+   * @return the system property name (e.g., google.cloud.project)
+   */
+  String getSystemProperty() {
+    return this.systemPropertyName;
+  }
+
+  /**
+   * Retrieves the configured value for this option. This method checks the environment variable
+   * first and then the system property.
+   *
+   * @return The configured value as a string, or throws an exception if not configured.
+   * @throws ConfigurationException if neither the environment variable nor the system property is
+   *     set.
+   */
+  String getConfiguredValue() {
+    String envVar = System.getenv(this.getEnvironmentVariable());
+    String sysProp = System.getProperty(this.getSystemProperty());
+
+    if (envVar != null && !envVar.isEmpty()) {
+      return envVar;
+    } else if (sysProp != null && !sysProp.isEmpty()) {
+      return sysProp;
+    } else {
+      throw new ConfigurationException(
+          String.format(
+              "GCP Authentication Extension not configured properly: %s not configured. Configure it by exporting environment variable %s or system property %s",
+              this.userReadableName, this.getEnvironmentVariable(), this.getSystemProperty()));
+    }
+  }
+
+  /**
+   * Retrieves the value for this option, prioritizing environment variables and system properties.
+   * If neither an environment variable nor a system property is set for this option, the provided
+   * fallback function is used to determine the value.
+   *
+   * @param fallback A {@link Supplier} that provides the default value for the option when it is
+   *     not explicitly configured via an environment variable or system property.
+   * @return The configured value for the option, obtained from the environment variable, system
+   *     property, or the fallback function, in that order of precedence.
+   */
+  String getConfiguredValueWithFallback(Supplier<String> fallback) {
+    try {
+      return this.getConfiguredValue();
+    } catch (ConfigurationException e) {
+      return fallback.get();
+    }
+  }
+}