Allow customisation of default security object

COUCHDB-3016
diff --git a/src/couch_db_updater.erl b/src/couch_db_updater.erl
index 813161a..28022a8 100644
--- a/src/couch_db_updater.erl
+++ b/src/couch_db_updater.erl
@@ -570,7 +570,7 @@
         [{compression, Compression}]),
     case couch_db_header:security_ptr(Header) of
     nil ->
-        Security = [],
+        Security = default_security_object(),
         SecurityPtr = nil;
     SecurityPtr ->
         {ok, Security} = couch_file:pread_term(Fd, SecurityPtr)
@@ -1437,3 +1437,12 @@
     end,
     SummaryBin = ?term_to_bin({Body, Atts}),
     couch_file:assemble_file_chunk(SummaryBin, couch_crypto:hash(md5, SummaryBin)).
+
+default_security_object() ->
+    case config:get("couchdb", "default_security", "open") of
+        "admin_only" ->
+            [{<<"members">>,{[{<<"roles">>,[<<"_admin">>]}]}},
+             {<<"admins">>,{[{<<"roles">>,[<<"_admin">>]}]}}];
+        "everyone" ->
+            []
+    end.