External Storage Save in session does not prompt for user login

Greetings,
Fresh install - new admin. Attempted to set up external storage accessed via SMB/CIFS. Wanted per user authentication so selected Login Credentials save in session. When A user attempts to access the external storage a "Storage not available" error is returned. If I add a username and password pair to the configuration in the admin panel it works fine - but then all my users are in the same login which is not what I require.

Shouldn't they be prompted for a login/password pair for the session? Or am i missing something I am not getting from checking the admin manual?

Please help us by providing the following info. Before posting please also check the pinned "Known issues" threads and make sure that you're running the latest available version for your oC release: https://owncloud.org/changelog/

Steps to reproduce
1.Create external storage accessed via SMB/CIFS
2.Select Log-in credentials save in session
3.user attempts to access the external storage - fails
4.Share and enjoy

Expected behaviour
Expected user to be prompted for login and password

Actual behaviour
No credential prompt - external storage unavailable

Server configuration
Operating system: Debian Jessie
Web server:2.4.10 (Debian)
Database: MySQL 5.5.54-0+deb8u1
PHP version:5.6.30-0+deb8u1
ownCloud version (see ownCloud admin page):
Updated from an older ownCloud or fresh install:Fresh install
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): External Storage

ownCloud log (data/owncloud.log)

Please paste possible errors in the following code block, see https://central.owncloud.org/t/how-to-find-webserver-or-oc-logfile-enable-php-logfile/808 for more info

Exception: {"Exception":"OCP\\Files\\StorageNotAvailableException","Message":"Invalid login","Code":0,"Trace":"#0 \/var\/www\/owncloud\/apps\/files_external\/lib\/Lib\/Storage\/SMB.php(279): OCA\\Files_External\\Lib\\Storage\\SMB->getFileInfo('')\n#1 \/var\/www\/owncloud\/lib\/private\/Files\/Storage\/Common.php(436): OCA\\Files_External\\Lib\\Storage\\SMB->stat('')\n#2 \/var\/www\/owncloud\/apps\/files_external\/lib\/Lib\/Storage\/SMB.php(616): OC\\Files\\Storage\\Common->test()\n#3 \/var\/www\/owncloud\/apps\/files_external\/lib\/config.php(231): OCA\\Files_External\\Lib\\Storage\\SMB->test(false, false)\n#4 \/var\/www\/owncloud\/apps\/files_external\/lib\/Controller\/StoragesController.php(255): OC_Mount_Config::getBackendStatus('\\\\OCA\\\\Files_Exte...', Array, false, false)\n#5 \/var\/www\/owncloud\/apps\/files_external\/lib\/Controller\/UserGlobalStoragesController.php(119): OCA\\Files_External\\Controller\\StoragesController->updateStorageStatus(Object(OCA\\Files_External\\Lib\\StorageConfig), false)\n#6 [internal function]: OCA\\Files_External\\Controller\\UserGlobalStoragesController->show(1, false)\n#7 \/var\/www\/owncloud\/lib\/private\/AppFramework\/Http\/Dispatcher.php(159): call_user_func_array(Array, Array)\n#8 \/var\/www\/owncloud\/lib\/private\/AppFramework\/Http\/Dispatcher.php(89): OC\\AppFramework\\Http\\Dispatcher->executeController(Object(OCA\\Files_External\\Controller\\UserGlobalStoragesController), 'show')\n#9 \/var\/www\/owncloud\/lib\/private\/AppFramework\/App.php(99): OC\\AppFramework\\Http\\Dispatcher->dispatch(Object(OCA\\Files_External\\Controller\\UserGlobalStoragesController), 'show')\n#10 \/var\/www\/owncloud\/lib\/private\/AppFramework\/Routing\/RouteActionHandler.php(46): OC\\AppFramework\\App::main('UserGlobalStora...', 'show', Object(OC\\AppFramework\\DependencyInjection\\DIContainer), Array)\n#11 [internal function]: OC\\AppFramework\\Routing\\RouteActionHandler->__invoke(Array)\n#12 \/var\/www\/owncloud\/lib\/private\/Route\/Router.php(280): call_user_func(Object(OC\\AppFramework\\Routing\\RouteActionHandler), Array)\n#13 \/var\/www\/owncloud\/lib\/base.php(891): OC\\Route\\Router->match('\/apps\/files_ext...')\n#14 \/var\/www\/owncloud\/index.php(54): OC::handleRequest()\n#15 {main}","File":"\/var\/www\/owncloud\/apps\/files_external\/lib\/Lib\/Storage\/SMB.php","Line":172}

Integrity status for oC9+

No errors have been found.