feat: Allow Impersonated SA Credentials to make requests authenticate…

…d with an IdToken

feat: Allow Impersonated SA Credentials to make requests authenticated with an IdToken

chore: Removed uncommented code

src/ApplicationDefaultCredentials.php

@@ -20,6 +20,7 @@
 use DomainException;
 use Google\Auth\Credentials\AppIdentityCredentials;
 use Google\Auth\Credentials\GCECredentials;
+use Google\Auth\Credentials\ImpersonatedServiceAccountCredentials;
 use Google\Auth\Credentials\ServiceAccountCredentials;
 use Google\Auth\HttpHandler\HttpClientCache;
 use Google\Auth\HttpHandler\HttpHandlerFactory;
@@ -302,11 +303,13 @@ public static function getIdTokenCredentials(
                 throw new InvalidArgumentException('ID tokens are not supported for end user credentials');
             }
 
-            if ($jsonKey['type'] != 'service_account') {
+            if (! in_array($jsonKey['type'], ['service_account', 'impersonated_service_account'])) {
                 throw new InvalidArgumentException('invalid value in the type field');
             }
 
-            $creds = new ServiceAccountCredentials(null, $jsonKey, null, $targetAudience);
+            $creds = $jsonKey['type'] === 'service_account'
+                ? new ServiceAccountCredentials(null, $jsonKey, null, $targetAudience)
+                : new ImpersonatedServiceAccountCredentials(null, $jsonKey, null, $targetAudience);
         } elseif (self::onGce($httpHandler, $cacheConfig, $cache)) {
             $creds = new GCECredentials(null, null, $targetAudience);
             $creds->setIsOnGce(true); // save the credentials a trip to the metadata server

src/Credentials/ImpersonatedServiceAccountCredentials.php

@@ -18,9 +18,16 @@
 
 namespace Google\Auth\Credentials;
 
+use Exception;
 use Google\Auth\CredentialsLoader;
+use Google\Auth\HttpHandler\HttpClientCache;
+use Google\Auth\HttpHandler\HttpHandlerFactory;
 use Google\Auth\IamSignerTrait;
+use Google\Auth\OAuth2;
 use Google\Auth\SignBlobInterface;
+use GuzzleHttp\Psr7\Request;
+use InvalidArgumentException;
+use Psr\Http\Message\RequestInterface;
 
 class ImpersonatedServiceAccountCredentials extends CredentialsLoader implements SignBlobInterface
 {
@@ -31,25 +38,37 @@ class ImpersonatedServiceAccountCredentials extends CredentialsLoader implements
     /**
      * @var string
      */
-    protected $impersonatedServiceAccountName;
+    protected string $impersonatedServiceAccountName;
 
     /**
      * @var UserRefreshCredentials
      */
-    protected $sourceCredentials;
+    protected UserRefreshCredentials $sourceCredentials;
+
+    /**
+     * @var array{target_audience?: string} Additional claims for the id token
+     */
+    protected array $additionalClaims;
 
     /**
      * Instantiate an instance of ImpersonatedServiceAccountCredentials from a credentials file that
      * has be created with the --impersonated-service-account flag.
      *
-     * @param string|string[]     $scope   The scope of the access request, expressed either as an
-     *                                     array or as a space-delimited string.
+     * @param string|string[]|null $scope The scope of the access request, expressed either as an
+     *   array or as a space-delimited string.
      * @param string|array<mixed> $jsonKey JSON credential file path or JSON credentials
-     *                                     as an associative array.
+     *   as an associative array.
+     * @param string|null $sub an email address account to impersonate, in situations when
+     *    the service account has been delegated domain wide access.
+     * @param string|null $targetAudience The audience for the ID token.
      */
     public function __construct(
-        $scope,
-        $jsonKey
+        string|array|null $scope,
+        string|array $jsonKey,
+        // sub is currently not implemented but specified to keep the order of arguments
+        // the same as ServiceAccountCredentials
+        string $sub = null,
+        string $targetAudience = null
     ) {
         if (is_string($jsonKey)) {
             if (!file_exists($jsonKey)) {
@@ -69,10 +88,21 @@ public function __construct(
             throw new \LogicException('json key is missing the source_credentials field');
         }
 
+        if ($scope && $targetAudience) {
+            throw new InvalidArgumentException(
+                'Scope and targetAudience cannot both be supplied'
+            );
+        }
+
         $this->impersonatedServiceAccountName = $this->getImpersonatedServiceAccountNameFromUrl(
             $jsonKey['service_account_impersonation_url']
         );
 
+        $this->additionalClaims = [];
+        if ($targetAudience) {
+            $this->additionalClaims = ['target_audience' => $targetAudience];
+        }
+
         $this->sourceCredentials = new UserRefreshCredentials(
             $scope,
             $jsonKey['source_credentials']
@@ -109,25 +139,61 @@ public function getClientName(callable $unusedHttpHandler = null)
     }
 
     /**
-     * @param callable $httpHandler
+     * Get an auth token.
      *
+     * @param callable $httpHandler
      * @return array<mixed> {
      *     A set of auth related metadata, containing the following
      *
      *     @type string $access_token
      *     @type int $expires_in
      *     @type string $scope
      *     @type string $token_type
-     *     @type string $id_token
+     *     @type ?string $id_token
      * }
+     * @throws Exception
      */
-    public function fetchAuthToken(callable $httpHandler = null)
+    public function fetchAuthToken(callable $httpHandler = null): array
     {
-        // We don't support id token endpoint requests as of now for Impersonated Cred
-        return $this->sourceCredentials->fetchAuthToken(
+        $tokens = $this->sourceCredentials->fetchAuthToken(
             $httpHandler,
             $this->applyTokenEndpointMetrics([], 'at')
         );
+
+        // the authRequestType='it' does not work
+        // fetch an id token using the access token from iam credentials
+        if (array_key_exists('target_audience', $this->additionalClaims)) {
+            if (is_null($httpHandler)) {
+                $httpHandler = HttpHandlerFactory::build(HttpClientCache::getHttpClient());
+            }
+
+            $impersonatedServiceAccount = $this->getClientName();
+            $request = new Request(
+                'POST',
+                "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/{$impersonatedServiceAccount}:generateIdToken",
+                [
+                    'Authorization' => "Bearer {$tokens['access_token']}",
+                    'Cache-Control' => 'no-store',
+                    'Content-Type' => 'application/json',
+                ],
+                json_encode([
+                    'audience' => $this->additionalClaims['target_audience'],
+                    'includeEmail' => true,
+                ])
+            );
+            $body = (string) $httpHandler($request)->getBody();
+
+            // Assume it's JSON; if it's not throw an exception
+            if (null === $res = json_decode($body, true)) {
+                throw new Exception('Invalid JSON response');
+            }
+            // we cannot append the id_token to the list of tokens already fetched
+            // as the AuthTokenMiddleware will first try to set the access_token if
+            // it can find it.
+            $tokens = ['id_token' => $res['token']];
+        }
+
+        return $tokens;
     }
 
     /**

src/Middleware/AuthTokenMiddleware.php

@@ -17,6 +17,7 @@
 
 namespace Google\Auth\Middleware;
 
+use Exception;
 use Google\Auth\FetchAuthTokenCache;
 use Google\Auth\FetchAuthTokenInterface;
 use Google\Auth\GetQuotaProjectInterface;
@@ -123,6 +124,7 @@ public function __invoke(callable $handler)
      *
      * @param RequestInterface $request
      * @return RequestInterface
+     * @throws Exception
      */
     private function addAuthHeaders(RequestInterface $request)
     {

tests/ApplicationDefaultCredentialsTest.php

@@ -21,6 +21,7 @@
 use Google\Auth\ApplicationDefaultCredentials;
 use Google\Auth\Credentials\ExternalAccountCredentials;
 use Google\Auth\Credentials\GCECredentials;
+use Google\Auth\Credentials\ImpersonatedServiceAccountCredentials;
 use Google\Auth\Credentials\ServiceAccountCredentials;
 use Google\Auth\CredentialsLoader;
 use Google\Auth\CredentialSource;
@@ -155,6 +156,13 @@ public function testGceCredentials()
         $this->assertStringContainsString('a+user+scope', $tokenUri);
     }
 
+    public function testGetIdTokenCredentialsCanFindImpersonatedServiceAccountCredentials()
+    {
+        putenv('GOOGLE_APPLICATION_CREDENTIALS=' . __DIR__ . '/fixtures3/impersonated_service_account_credentials.json');
+        $creds = ApplicationDefaultCredentials::getIdTokenCredentials('123@456.com');
+        $this->assertInstanceOf(ImpersonatedServiceAccountCredentials::class, $creds);
+    }
+
     public function testImpersonatedServiceAccountCredentials()
     {
         putenv('HOME=' . __DIR__ . '/fixtures5');

tests/Credentials/ImpersonatedServiceAccountCredentialsTest.php

@@ -19,24 +19,25 @@
 namespace Google\Auth\Tests\Credentials;
 
 use Google\Auth\Credentials\ImpersonatedServiceAccountCredentials;
+use Google\Auth\Credentials\UserRefreshCredentials;
+use Google\Auth\Middleware\AuthTokenMiddleware;
+use GuzzleHttp\Psr7\Request;
+use GuzzleHttp\Psr7\Response;
 use LogicException;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\StreamInterface;
 
 class ImpersonatedServiceAccountCredentialsTest extends TestCase
 {
+    use ProphecyTrait;
+
     // Creates a standard JSON auth object for testing.
     private function createISACTestJson()
     {
-        return [
-            'type' => 'impersonated_service_account',
-            'service_account_impersonation_url' => 'https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/test@test-project.iam.gserviceaccount.com:generateAccessToken',
-            'source_credentials' => [
-                'client_id' => 'client123',
-                'client_secret' => 'clientSecret123',
-                'refresh_token' => 'refreshToken123',
-                'type' => 'authorized_user',
-            ]
-        ];
+        return json_decode(file_get_contents(__DIR__ . '/../fixtures3/impersonated_service_account_credentials.json'), true);
     }
 
     public function testGetServiceAccountNameEmail()
@@ -69,4 +70,76 @@ public function testErrorCredentials()
         $this->expectException(LogicException::class);
         new ImpersonatedServiceAccountCredentials($scope, $testJson['source_credentials']);
     }
+
+    public function testGetIdToken()
+    {
+        $testJson = $this->createISACTestJson();
+        $targetAudience = '123@456.com';
+        $creds = new ImpersonatedServiceAccountCredentials(null, $testJson, null, $targetAudience);
+
+        $requestCount = 0;
+        // getting an id token will take two requests
+        $httpHandler = function (RequestInterface $request) use (&$requestCount, $creds) {
+            $impersonatedServiceAccount = $creds->getClientName();
+
+            $responseBody = '';
+            switch (++$requestCount) {
+                case 1: // the call to swap the refresh token for an access token
+                    $this->assertEquals(UserRefreshCredentials::TOKEN_CREDENTIAL_URI, (string) $request->getUri());
+                    $responseBody = '{"access_token":"this is an access token"}';
+                    break;
+
+                case 2: // the call to swap the access token for an id token
+                    $this->assertEquals("https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/{$impersonatedServiceAccount}:generateIdToken", (string) $request->getUri());
+                    $authHeader = $request->getHeader('authorization');
+                    $this->assertCount(1, $authHeader);
+                    $this->assertEquals('Bearer this is an access token', $authHeader[0]);
+                    $responseBody = '{"token": "this is the id token"}';
+                    break;
+            }
+
+            $body = $this->prophesize(StreamInterface::class);
+            $body->__toString()->willReturn($responseBody);
+
+            $response = $this->prophesize(ResponseInterface::class);
+            $response->getBody()->willReturn($body->reveal());
+            $response->hasHeader('Content-Type')->willReturn(true);
+            $response->getHeaderLine('Content-Type')->willReturn('application/json');
+
+            if ($requestCount === 2) {
+                $response->hasHeader('Content-Type')->willReturn(false);
+            }
+
+            return $response->reveal();
+        };
+
+        $creds->fetchAuthToken($httpHandler);
+        // any checks on the result are futile as they have been coded above
+    }
+    public function testCanBeUsedInAuthTokenMiddlewareWhenAnAudienceIsGiven()
+    {
+        $targetAudience = '123@456.com';
+        $jsonKey = $this->createISACTestJson();
+        $credentials = new ImpersonatedServiceAccountCredentials(null, $jsonKey, null, $targetAudience);
+
+        // this handler is for the middleware constructor, which will pass it to the ISAC to fetch tokens
+        $httpHandler = getHandler([
+            new Response(200, ['Content-Type' => 'application/json'], '{"access_token":"this.is.an.access.token"}'),
+            new Response(200, ['Content-Type' => 'application/json'], '{"token":"this.is.an.id.token"}'),
+        ]);
+        $middleware = new AuthTokenMiddleware($credentials, $httpHandler);
+
+        // this handler is the actual handler that makes the authenticated request
+        $httpHandler = function (RequestInterface $request) use (&$requestCount) {
+            $this->assertTrue($request->hasHeader('authorization'));
+            $authHeader = $request->getHeader('authorization');
+            $this->assertCount(1, $authHeader);
+            $this->assertEquals('Bearer this.is.an.id.token', $authHeader[0]);
+        };
+
+        $middleware($httpHandler)(
+            new Request('GET', 'https://www.google.com'),
+            ['auth' => 'google_auth']
+        );
+    }
 }

tests/FetchAuthTokenTest.php

@@ -109,6 +109,7 @@ public function provideMakeHttpClient()
             ['Google\Auth\Credentials\AppIdentityCredentials'],
             ['Google\Auth\Credentials\GCECredentials'],
             ['Google\Auth\Credentials\ServiceAccountCredentials'],
+            ['Google\Auth\Credentials\ImpersonatedServiceAccountCredentials'],
             ['Google\Auth\Credentials\ServiceAccountJwtAccessCredentials'],
             ['Google\Auth\Credentials\UserRefreshCredentials'],
             ['Google\Auth\OAuth2'],

tests/fixtures3/impersonated_service_account_credentials.json

@@ -0,0 +1,10 @@
+{
+  "type": "impersonated_service_account",
+  "service_account_impersonation_url": "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/test@test-project.iam.gserviceaccount.com:generateAccessToken",
+  "source_credentials": {
+    "client_id": "client123",
+    "client_secret": "clientSecret123",
+    "refresh_token": "refreshToken123",
+    "type": "authorized_user"
+  }
+}