diff -r 3a01bd8e3f8c -r 8ec06aff386e structs.go
--- a/structs.go	Sun Dec 16 17:10:21 2012 -0700
+++ b/structs.go	Sun Dec 16 19:54:54 2012 -0700
@@ -74,7 +74,7 @@
 type auth struct {
 	XMLName   xml.Name
 	Chardata  string `xml:",chardata"`
-	Mechanism string `xml:"mechanism,attr"`
+	Mechanism string `xml:"mechanism,attr,omitempty"`
 	Any       *Generic
 }