Allow user backends to provide quotas

lib/private/User/Manager.php

@@ -393,6 +393,12 @@ private function newAccount($uid, $backend) {
 				$account->setEmail($email);
 			}
 		}
+		if ($backend instanceof IProvidesQuotaBackend) {
+			$quota = $backend->getQuota($uid);
+			if ($quota !== null) {
+				$account->setQuota($quota);
+			}
+		}
 		$home = false;
 		if ($backend->implementsActions(Backend::GET_HOME)) {
 			$home = $backend->getHome($uid);

lib/public/User/IProvidesQuotaBackend.php

@@ -0,0 +1,44 @@
+<?php
+/**
+ * @author Vincent Petry <pvince81@owncloud.com>
+ *
+ * @copyright Copyright (c) 2017, ownCloud GmbH
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+
+// use OCP namespace for all classes that are considered public.
+// This means that they should be used by apps instead of the internal ownCloud classes
+namespace OCP\User;
+
+/**
+ * Interface IProvidesQuotaBackend
+ *
+ * @package OCP\User
+ * @since 10.0
+ */
+interface IProvidesQuotaBackend {
+
+	/**
+	 * Get a users quota
+	 *
+	 * @param string $uid The username
+	 * @return string
+	 * @since 10.0
+	 */
+	public function getQuota($uid);
+}
+