--- loncom/auth/lonacc.pm	2014/12/01 22:52:54	1.160
+++ loncom/auth/lonacc.pm	2015/01/23 15:44:20	1.161
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # Cookie Based Access Handler
 #
-# $Id: lonacc.pm,v 1.160 2014/12/01 22:52:54 raeburn Exp $
+# $Id: lonacc.pm,v 1.161 2015/01/23 15:44:20 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -290,7 +290,10 @@ sub sso_login {
 	return undef;
     }
 
-    my ($user) = ($r->user =~ m/([a-zA-Z0-9_\-@.]*)/);
+    my ($user) = ($r->user =~ m/^($match_username)$/);
+    if ($user eq '') {
+        return undef;
+    }
 
     my $query = $r->args;
     my %form;