Refactored to use functions rather than App Engine apps, added tests,…

… added README

auth/README.md

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+# Google Auth PHP Sample Application
+
+## Description
+
+This command-line application shows how to authenticate to Google Cloud APIs
+using different methods. This sample uses Storage as an example, but these
+methods will work on any Google Cloud API.
+
+## Build and Run
+1.  **Enable APIs** - [Enable the Storage API](https://console.cloud.google.com/flows/enableapi?apiid=storage-api.googleapis.com)
+    and create a new project or select an existing project.
+2.  **Download The Credentials** - Click "Go to credentials" after enabling the APIs. Click "New Credentials"
+    and select "Service Account Key". Create a new service account, use the JSON key type, and
+    select "Create". Once downloaded, set the environment variable `GOOGLE_APPLICATION_CREDENTIALS`
+    to the path of the JSON key that was downloaded.
+3.  **Clone the repo** and cd into this directory
+```
+    $ git clone https://github.com/GoogleCloudPlatform/php-docs-samples
+    $ cd php-docs-samples/auth
+```
+4.  **Install dependencies** via [Composer](http://getcomposer.org/doc/00-intro.md).
+    Run `php composer.phar install` (if composer is installed locally) or `composer install`
+    (if composer is installed globally).
+5.  Run `php auth.php`. The following commands are available and work on command line:
+```
+  auth-cloud-implicit                      Authenticate to a cloud client library using a service account implicitly.
+  auth-cloud-explicit                      Authenticate to a cloud client library using a service account explicitly.
+```
+6. The following commands are available but will throw a ServiceException when
+run from command-line. The Compute Engine method only works on Compute Engine,
+App Engine Flexible, Cloud Functions, and Container Engine. The App Engine
+method only works on App Engine Standard.
+```
+  auth-cloud-explicit-compute-engine       Authenticate to a cloud client library using Compute Engine credentials explicitly.
+  auth-cloud-explicit-app-engine           Authenticate to a cloud client library using App Engine Standard credentials explicitly.
+```
+7. Run `php auth.php COMMAND --help` to print information about the usage of each command.
+
+## Contributing changes
+
+* See [CONTRIBUTING.md](../../CONTRIBUTING.md)
+
+## Licensing
+
+* See [LICENSE](../../LICENSE)