Index: src/main/java/com/xpn/xwiki/user/impl/xwiki/XWikiGroupServiceImpl.java
===================================================================
--- src/main/java/com/xpn/xwiki/user/impl/xwiki/XWikiGroupServiceImpl.java	(revision 19222)
+++ src/main/java/com/xpn/xwiki/user/impl/xwiki/XWikiGroupServiceImpl.java	(working copy)
@@ -154,6 +154,11 @@
         }
     }
 
+    protected boolean isAllGroupImplicit(XWikiContext context) {
+       long  implicit = context.getWiki().ParamAsLong("xwiki.authentication.group.allgroupimplicit", 0);
+       return (implicit==1);
+    }
+
     public Collection<String> listGroupsForUser(String username, XWikiContext context) throws XWikiException
     {
         List<String> list = null;
@@ -179,6 +184,16 @@
                     } catch (QueryException ex) {
                         throw new XWikiException(0, 0, ex.getMessage(), ex);
                     }
+
+                    if (isAllGroupImplicit(context)
+                         &&!username.equals("XWiki.XWikiAllGroup")
+                         &&!username.equals("xwiki:XWiki.XWikiAllGroup") 
+                         &&!username.equals("XWiki.XWikiGuest")
+                         &&!username.equals("xwiki:XWiki.XWikiGuest")) {
+                         if (!list.contains("XWiki.XWikiAllGroup"))
+                            list.add("XWiki.XWikiAllGroup");
+                    }
+
                     this.groupCache.set(key, list);
                 }
             }