Fixed bug in issue #9 on github
https://github.com/jaredhanson/passport-http/issues/9
"Submitting empty string for username in Digest auth will return a 400, instead of a 401."

Added test case to validate empty username
Merge pull request #10 from davidpodolsky/master

Fixed issue where submitting empty string for username in Digest auth will return a 400, instead of a 401. Added empty user test case.