Enables Google Authentication for YOURLS

Proper documentation coming soon.

For now, here is the very rough documentation:

1. Download the plugin, move contents to plugins directory and rename to google-auth/
2. Download and configure Google APIs Client Library for PHP
   • See https://github.com/google/google-api-php-client for install instructions.
   • The code assumes that the API directory (vendor/) will reside inside the google-auth/ plugin directory
3. Create an OAuth 2.0 client ID, and download the resulting JSON file (client_secrets.json)
   • See https://developers.google.com/api-client-library/php/auth/web-app
   • place the client secrets file inside the google-auth/ plugin directory
4. This plugin allows you to filter access based on domain (i.e. only @mydomain.com addresses)
   • Edit define('APPROVED_DOMAIN', "mydomain.com");
   • If you want anyone with a Google account to get in (you probably don't want that), set to *
     • i.e. define('APPROVED_DOMAIN', "*");