Add Oauth 2 support

Grant Types are configured outside the lib and our Config object hooks
its all up for easy peasy Oauth 2.

Author: rdohms

composer.json

@@ -15,18 +15,20 @@
         "guzzlehttp/guzzle-services": "^1.1",
         "gimler/guzzle-description-loader": "^0.0.4"
     },
-
+    
     "require-dev": {
         "symfony/css-selector": "~2.2",
         "symfony/dom-crawler": "~2.2",
         "symfony/console": "~2.2",
         "phpunit/phpunit": "^4.8",
         "symfony/var-dumper": "~2.6",
         "mathiasgrimm/arraypath": "~1.3",
-        "guzzlehttp/oauth-subscriber": "^0.3.0"
+        "guzzlehttp/oauth-subscriber": "^0.3.0",
+        "kamermans/guzzle-oauth2-subscriber": "^1.0"
     },
     "suggest": {
-        "guzzlehttp/oauth-subscriber": "For authenticating with Oauth1.0"
+        "guzzlehttp/oauth-subscriber": "For authenticating with Oauth1.0",
+        "kamermans/guzzle-oauth2-subscriber": "For authenticating with OAuth2"
     },
 
     "autoload": {

composer.lock

@@ -0,0 +1,53 @@
+<?php
+
+namespace DMS\Service\Meetup\Config;
+
+use kamermans\OAuth2\GrantType\GrantTypeInterface;
+use kamermans\OAuth2\OAuth2Middleware;
+
+final class OAuth2Config implements ClientConfig
+{
+    /**
+     * @var GrantTypeInterface
+     */
+    protected $grantType;
+
+    /**
+     * @var bool
+     */
+    protected $shouldSignAllRequests;
+
+    /**
+     * @param GrantTypeInterface $grantType
+     * @param bool               $shouldSignAllRequests
+     */
+    public function __construct(GrantTypeInterface $grantType, bool $shouldSignAllRequests = true)
+    {
+        $this->grantType             = $grantType;
+        $this->shouldSignAllRequests = $shouldSignAllRequests;
+    }
+
+    /**
+     * @return callable[]
+     */
+    public function getMiddleware(): array
+    {
+        return [
+            'oauth2' => new OAuth2Middleware($this->grantType)
+        ];
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getClientConfig(): array
+    {
+        $config = [];
+
+        if ($this->shouldSignAllRequests) {
+            $config['auth'] = 'oauth';
+        }
+
+        return $config;
+    }
+}