--- vendor/laravel/framework/src/Illuminate/Auth/EloquentUserProvider.orig.php	2018-07-25 22:46:46.980782012 +0200
+++ vendor/laravel/framework/src/Illuminate/Auth/EloquentUserProvider.php	2018-07-25 22:48:47.490981175 +0200
@@ -121,7 +121,7 @@
             if (is_array($value) || $value instanceof Arrayable) {
                 $query->whereIn($key, $value);
             } else {
-                $query->where($key, $value);
+                $query->whereRaw('LOWER(' . $key . ')=LOWER(?)', [$value]);
             }
         }