Allow empty passwords as per http://forum.springframework.org/viewtopic.php?p=13343.

core/src/main/java/org/acegisecurity/userdetails/User.java

@@ -1,4 +1,4 @@
-/* Copyright 2004 Acegi Technology Pty Limited
+/* Copyright 2004, 2005 Acegi Technology Pty Limited
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -93,7 +93,7 @@ public class User implements UserDetails {
         boolean accountNonExpired, boolean credentialsNonExpired,
         GrantedAuthority[] authorities) throws IllegalArgumentException {
         if (((username == null) || "".equals(username)) || (password == null)
-            || "".equals(password) || (authorities == null)) {
+            || (authorities == null)) {
             throw new IllegalArgumentException(
                 "Cannot pass null or empty values to constructor");
         }