Add docker image and config for local SSO IdP (#2001)

dev/authsources.php.example

@@ -0,0 +1,20 @@
+<?php
+
+$config = array(
+    'admin' => array(
+        'core:AdminPassword',
+    ),
+
+    'example-userpass' => array(
+        'exampleauth:UserPass',
+        'user1:password' => array(
+            'email' => 'user1@example.com',
+            'uid' => array('user1'),
+        ),
+        'user2:password' => array(
+            'email' => 'user2@example.com',
+            'uid' => array('user2'),
+        ),
+    ),
+
+);