diff --git a/.travis.yml b/.travis.yml
index c8171155a..a7fa91a57 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -58,3 +58,8 @@ script:
     else
       vendor/bin/phpunit;
     fi
+
+cache:
+  directories:
+    - vendor
+    - "$HOME/.composer/cache"
diff --git a/README.md b/README.md
index eea62eef1..977901cc7 100644
--- a/README.md
+++ b/README.md
@@ -1,150 +1,8 @@
-# Google Auth Library for PHP
+# Google Auth Library for [Firebase PHP](https://github.com/firebase-php/firebase-php)
 
-<dl>
-  <dt>Homepage</dt><dd><a href="http://www.github.com/google/google-auth-library-php">http://www.github.com/google/google-auth-library-php</a></dd>
-  <dt>Authors</dt>
-    <dd><a href="mailto:temiola@google.com">Tim Emiola</a></dd>
-    <dd><a href="mailto:stanleycheung@google.com">Stanley Cheung</a></dd>
-    <dd><a href="mailto:betterbrent@google.com">Brent Shaffer</a></dd>
-  <dt>Copyright</dt><dd>Copyright © 2015 Google, Inc.</dd>
-  <dt>License</dt><dd>Apache 2.0</dd>
-</dl>
+[![Build Status](https://travis-ci.org/firebase-php/google-auth-library-php.svg?branch=master)](https://travis-ci.org/firebase-php/google-auth-library-php)
 
-## Description
+> This is a fork from [Google Auth Library for PHP](https://github.com/googleapis/google-auth-library-php) which is internally used in [Firebase PHP](https://github.com/firebase-php/firebase-php)
 
-This is Google's officially supported PHP client library for using OAuth 2.0
-authorization and authentication with Google APIs.
-
-### Installing via Composer
-
-The recommended way to install the google auth library is through
-[Composer](http://getcomposer.org).
-
-```bash
-# Install Composer
-curl -sS https://getcomposer.org/installer | php
-```
-
-Next, run the Composer command to install the latest stable version:
-
-```bash
-composer.phar require google/auth
-```
-
-## Application Default Credentials
-
-This library provides an implementation of
-[application default credentials][application default credentials] for PHP.
-
-The Application Default Credentials provide a simple way to get authorization
-credentials for use in calling Google APIs.
-
-They are best suited for cases when the call needs to have the same identity
-and authorization level for the application independent of the user. This is
-the recommended approach to authorize calls to Cloud APIs, particularly when
-you're building an application that uses Google Compute Engine.
-
-#### Download your Service Account Credentials JSON file
-
-To use `Application Default Credentials`, You first need to download a set of
-JSON credentials for your project. Go to **APIs & Services** > **Credentials** in
-the [Google Developers Console][developer console] and select
-**Service account** from the **Add credentials** dropdown.
-
-> This file is your *only copy* of these credentials. It should never be
-> committed with your source code, and should be stored securely.
-
-Once downloaded, store the path to this file in the
-`GOOGLE_APPLICATION_CREDENTIALS` environment variable.
-
-```php
-putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/my/credentials.json');
-```
-
-> PHP's `putenv` function is just one way to set an environment variable.
-> Consider using `.htaccess` or apache configuration files as well.
-
-#### Enable the API you want to use
-
-Before making your API call, you must be sure the API you're calling has been
-enabled. Go to **APIs & Auth** > **APIs** in the
-[Google Developers Console][developer console] and enable the APIs you'd like to
-call. For the example below, you must enable the `Drive API`.
-
-#### Call the APIs
-
-As long as you update the environment variable below to point to *your* JSON
-credentials file, the following code should output a list of your Drive files.
-
-```php
-use Google\Auth\ApplicationDefaultCredentials;
-use GuzzleHttp\Client;
-use GuzzleHttp\HandlerStack;
-
-// specify the path to your application credentials
-putenv('GOOGLE_APPLICATION_CREDENTIALS=/path/to/my/credentials.json');
-
-// define the scopes for your API call
-$scopes = ['https://www.googleapis.com/auth/drive.readonly'];
-
-// create middleware
-$middleware = ApplicationDefaultCredentials::getMiddleware($scopes);
-$stack = HandlerStack::create();
-$stack->push($middleware);
-
-// create the HTTP client
-$client = new Client([
-  'handler' => $stack,
-  'base_uri' => 'https://www.googleapis.com',
-  'auth' => 'google_auth'  // authorize all requests
-]);
-
-// make the request
-$response = $client->get('drive/v2/files');
-
-// show the result!
-print_r((string) $response->getBody());
-```
-
-##### Guzzle 5 Compatibility
-
-If you are using [Guzzle 5][Guzzle 5], replace the `create middleware` and
-`create the HTTP Client` steps with the following:
-
-```php
-// create the HTTP client
-$client = new Client([
-  'base_url' => 'https://www.googleapis.com',
-  'auth' => 'google_auth'  // authorize all requests
-]);
-
-// create subscriber
-$subscriber = ApplicationDefaultCredentials::getSubscriber($scopes);
-$client->getEmitter()->attach($subscriber);
-
-```
-
-## License
-
-This library is licensed under Apache 2.0. Full license text is
-available in [COPYING][copying].
-
-## Contributing
-
-See [CONTRIBUTING][contributing].
-
-## Support
-
-Please
-[report bugs at the project on Github](https://github.com/google/google-auth-library-php/issues). Don't
-hesitate to
-[ask questions](http://stackoverflow.com/questions/tagged/google-auth-library-php)
-about the client or APIs on [StackOverflow](http://stackoverflow.com).
-
-[google-apis-php-client]: https://github.com/google/google-api-php-client
-[application default credentials]: https://developers.google.com/accounts/docs/application-default-credentials
-[contributing]: https://github.com/google/google-auth-library-php/tree/master/.github/CONTRIBUTING.md
-[copying]: https://github.com/google/google-auth-library-php/tree/master/COPYING
-[Guzzle]: https://github.com/guzzle/guzzle
-[Guzzle 5]: http://docs.guzzlephp.org/en/5.3
-[developer console]: https://console.developers.google.com
+### What's changed
+- Allow to get Project ID from ServiceAccountCredentials
diff --git a/composer.json b/composer.json
index e8da51d80..277ae52b9 100644
--- a/composer.json
+++ b/composer.json
@@ -1,9 +1,9 @@
 {
-  "name": "google/auth",
+  "name": "firebase-php/google-auth",
   "type": "library",
-  "description": "Google Auth Library for PHP",
-  "keywords": ["google", "oauth2", "authentication"],
-  "homepage": "http://github.com/google/google-auth-library-php",
+  "description": "A fork of Google Auth Library used in Firebase PHP project",
+  "keywords": ["google", "oauth2", "authentication", "firebase-php"],
+  "homepage": "http://github.com/firebase-php/google-auth",
   "license": "Apache-2.0",
   "require": {
     "php": ">=5.4",
diff --git a/src/Credentials/ServiceAccountCredentials.php b/src/Credentials/ServiceAccountCredentials.php
index 7e801b759..bfcd8f617 100644
--- a/src/Credentials/ServiceAccountCredentials.php
+++ b/src/Credentials/ServiceAccountCredentials.php
@@ -66,6 +66,11 @@ class ServiceAccountCredentials extends CredentialsLoader implements SignBlobInt
      */
     protected $auth;
 
+    /**
+     * @var string|null
+     */
+    private $projectId;
+
     /**
      * Create a new ServiceAccountCredentials.
      *
@@ -98,6 +103,7 @@ public function __construct(
             throw new \InvalidArgumentException(
                 'json key is missing the private_key field');
         }
+        $this->projectId = isset($jsonKey['project_id']) ? $jsonKey['project_id'] : null;
         $this->auth = new OAuth2([
             'audience' => self::TOKEN_CREDENTIAL_URI,
             'issuer' => $jsonKey['client_email'],
@@ -195,4 +201,9 @@ public function getClientName(callable $httpHandler = null)
     {
         return $this->auth->getIssuer();
     }
+
+    public function getProjectId()
+    {
+        return $this->projectId;
+    }
 }