Add google/auth and related libraries, and update other dependencies

common/vendor/google/auth/src/GetQuotaProjectInterface.php

@@ -0,0 +1,33 @@
+<?php
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace Google\Auth;
+
+/**
+ * An interface implemented by objects that can get quota projects.
+ */
+interface GetQuotaProjectInterface
+{
+    const X_GOOG_USER_PROJECT_HEADER = 'X-Goog-User-Project';
+
+    /**
+     * Get the quota project used for this API request
+     *
+     * @return string|null
+     */
+    public function getQuotaProject();
+}