Updated response to send a 401 if the user isn't found.

The server was actually throwing a 500 Internal Server Error with a full
stacktrace and a message of "User Not Authenticated."  Apparently, the
calling trace doesn't handle the HttpResponses.error correctly and the
exception bubbles all the way up.
Merge pull request #2 from mikesir87/authorizationFix

Updated response to send a 401 if the user isn't found.