Added AuthenticationSource abstract class

src/ncc/Abstracts/AuthenticationSource.php

@@ -0,0 +1,12 @@
+<?php
+
+    namespace ncc\Abstracts;
+
+    abstract class AuthenticationSource
+    {
+        const None = 'NONE';
+
+        const ServerProvided = 'SERVER_PROVIDED';
+
+        const UserProvided = 'USER_PROVIDED';
+    }