Add support for finding a user by external ID.

resources/lang/en/exceptions.php

@@ -60,4 +60,7 @@ return [
         'no_viable_nodes' => 'No nodes satisfying the requirements specified for automatic deployment could be found.',
         'no_viable_allocations' => 'No allocations satisfying the requirements for automatic deployment were found.',
     ],
+    'api' => [
+        'resource_not_found' => 'The requested resource does not exist on this server.',
+    ],
 ];