w3c validator with authtype = digest

Good day, sirs.
 
I have a question for you. One of our instructors is using w3c validator for her classes. However, we are using authtype = digest instead of basic for authentication for each individual student's webpages. And looks like the w3c validator does not work. When we change to basic, everything works great but when we switch to digest, we got errors:
 
I got the following unexpected response when trying to retrieve <http://cois-linux.austincc.edu/~dwh/>: 

400 Bad Request
 
Thanks for the help in advance.
 
We are using 2.2.3 apache server.
 
Duen-wen Hsiao
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