With the latest update of the git-client-plugin the default behavior is to use the JGit implementation instead of the git command line tool. For the git command line tool I set up HTTP authentication using the file .netrc in the home directory of Jenkins. This does not work anymore with the default JGit implementation. I had to switch back to the git command line tool, which is pretty annoying because the system property needs to be added to the JVM options of every slave.