When invoking hudson.Main with the name of a an external job and the path to the
script or program to run as arguments 1 and 2, a "Authentication required" error
message is given if hudson requires authentication. This is true even if the
HUDSON_HOME environment variable has the username and password in it.

A workaround is to not use hudson.Main, but another program, such as "curl" to
send the data as a POST and to provide the authentication credentials...