Index: java/org/apache/catalina/authenticator/FormAuthenticator.java
===================================================================
--- java/org/apache/catalina/authenticator/FormAuthenticator.java	(revision 1065026)
+++ java/org/apache/catalina/authenticator/FormAuthenticator.java	(working copy)
@@ -246,8 +246,9 @@
             return (false);
         }
 
-        // Yes -- Validate the specified credentials and redirect
-        // to the error page if they are not correct
+        // Yes -- Acknowledge the request, validate the specified credentials
+        // and redirect to the error page if they are not correct
+        response.sendAcknowledgement();
         Realm realm = context.getRealm();
         if (characterEncoding != null) {
             request.setCharacterEncoding(characterEncoding);
@@ -511,6 +512,9 @@
         }
 
         if ("POST".equalsIgnoreCase(request.getMethod())) {
+            // May need to acknowledge a 100-continue expectation
+            request.getResponse().sendAcknowledgement();
+
             ByteChunk body = new ByteChunk();
             body.setLimit(request.getConnector().getMaxSavePostSize());