Add Google authentication

vendor/OAuth/Common/Http/Client/ClientInterface.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace OAuth\Common\Http\Client;
+
+use OAuth\Common\Http\Uri\UriInterface;
+use OAuth\Common\Http\Exception\TokenResponseException;
+
+/**
+ * Any HTTP clients to be used with the library should implement this interface.
+ */
+interface ClientInterface
+{
+    /**
+     * Any implementing HTTP providers should send a request to the provided endpoint with the parameters.
+     * They should return, in string form, the response body and throw an exception on error.
+     *
+     * @param UriInterface $endpoint
+     * @param mixed        $requestBody
+     * @param array        $extraHeaders
+     * @param string       $method
+     *
+     * @return string
+     *
+     * @throws TokenResponseException
+     */
+    public function retrieveResponse(
+        UriInterface $endpoint,
+        $requestBody,
+        array $extraHeaders = array(),
+        $method = 'POST'
+    );
+}