feat: implement quota project from env var in google/auth

src/ApplicationDefaultCredentials.php

@@ -170,6 +170,11 @@ public static function getCredentials(
             $httpHandler = HttpHandlerFactory::build($client);
         }
 
+        if (is_null($quotaProject)) {
+            // if a quota project isn't specified, try to get one from the env var
+            $quotaProject = CredentialsLoader::quotaProjectFromEnv();
+        }
+
         if (!is_null($jsonKey)) {
             if ($quotaProject) {
                 $jsonKey['quota_project_id'] = $quotaProject;

src/CredentialsLoader.php

@@ -34,6 +34,7 @@ abstract class CredentialsLoader implements
 {
     const TOKEN_CREDENTIAL_URI = 'https://oauth2.googleapis.com/token';
     const ENV_VAR = 'GOOGLE_APPLICATION_CREDENTIALS';
+    const QUOTA_PROJECT_ENV_VAR = 'GOOGLE_CLOUD_QUOTA_PROJECT';
     const WELL_KNOWN_PATH = 'gcloud/application_default_credentials.json';
     const NON_WINDOWS_WELL_KNOWN_PATH_BASE = '.config';
     const MTLS_WELL_KNOWN_PATH = '.secureConnect/context_aware_metadata.json';
@@ -227,6 +228,18 @@ public function updateMetadata(
         return $metadata_copy;
     }
 
+    /**
+     * Fetch a quota project from the environment variable
+     * GOOGLE_CLOUD_QUOTA_PROJECT. Return null if
+     * GOOGLE_CLOUD_QUOTA_PROJECT is not specified.
+     *
+     * @return string|null
+     */
+    public static function quotaProjectFromEnv()
+    {
+        return getenv(self::QUOTA_PROJECT_ENV_VAR) ?: null;
+    }
+
     /**
      * Gets a callable which returns the default device certification.
      *

src/OAuth2.php

@@ -1348,7 +1348,8 @@ public function setIdToken($idToken)
     }
 
     /**
-     * Get the granted scopes (if they exist) for the last fetched token.
+     * Get the granted space-separated scopes (if they exist) for the last
+     * fetched token.
      *
      * @return string|null
      */

tests/ApplicationDefaultCredentialsTest.php

@@ -21,6 +21,7 @@
 use Google\Auth\ApplicationDefaultCredentials;
 use Google\Auth\Credentials\GCECredentials;
 use Google\Auth\Credentials\ServiceAccountCredentials;
+use Google\Auth\CredentialsLoader;
 use Google\Auth\GCECache;
 use GuzzleHttp\Psr7;
 use GuzzleHttp\Psr7\Response;
@@ -590,6 +591,59 @@ public function testGetCredentialsUtilizesQuotaProjectInKeyFile()
         );
     }
 
+    /** @runInSeparateProcess */
+    public function testGetCredentialsUtilizesQuotaProjectEnvVar()
+    {
+        $quotaProject = 'quota-project-from-env-var';
+        putenv(CredentialsLoader::QUOTA_PROJECT_ENV_VAR . '=' . $quotaProject);
+        putenv('HOME=' . __DIR__ . '/fixtures');
+
+        $credentials = ApplicationDefaultCredentials::getCredentials();
+
+        $this->assertEquals(
+            $quotaProject,
+            $credentials->getQuotaProject()
+        );
+    }
+
+    /** @runInSeparateProcess */
+    public function testGetCredentialsUtilizesQuotaProjectParameterOverEnvVar()
+    {
+        $quotaProject = 'quota-project-from-parameter';
+        putenv(CredentialsLoader::QUOTA_PROJECT_ENV_VAR . '=quota-project-from-env-var');
+        putenv('HOME=' . __DIR__ . '/fixtures');
+
+        $credentials = ApplicationDefaultCredentials::getCredentials(
+            null, // $scope
+            null, // $httpHandler
+            null, // $cacheConfig
+            null, // $cache
+            $quotaProject, // $quotaProject
+            null  // $defaultScope
+        );
+
+        $this->assertEquals(
+            $quotaProject,
+            $credentials->getQuotaProject()
+        );
+    }
+
+    /** @runInSeparateProcess */
+    public function testGetCredentialsUtilizesQuotaProjectEnvVarOverKeyFile()
+    {
+        $quotaProject = 'quota-project-from-env-var';
+        $keyFile = __DIR__ . '/fixtures' . '/private.json';
+        putenv(CredentialsLoader::QUOTA_PROJECT_ENV_VAR . '=' . $quotaProject);
+        putenv(CredentialsLoader::ENV_VAR . '=' . $keyFile);
+
+        $credentials = ApplicationDefaultCredentials::getCredentials();
+
+        $this->assertEquals(
+            $quotaProject,
+            $credentials->getQuotaProject()
+        );
+    }
+
     public function testWithFetchAuthTokenCacheAndExplicitQuotaProject()
     {
         $keyFile = __DIR__ . '/fixtures' . '/private.json';