Using etc/ant_configuration/user.properties I encountered some issues.
Most notably there was a problem with user names beginning with a lower-case letter. Basically the user generation works but the user name in the created xml file starts with an upper-case letter which is presumably the reason why later the user authentication failed.
Additionally, there seems to be some issue with passwords that do not contain more than 2 characters.
I believe I tried user "user" and password "pw".