BTW the LuaTeX source isn't really hidden; there's an unofficial GitHub mirror at https://github.com/TeX-Live/luatex (or look at https://github.com/TeX-Live/texlive-source/tree/trunk/texk/w... specifically) and for their official SVN repository at https://serveur-svn.lri.fr/svn/modhel/luatex the username/password (anonsvn/anonsvn) are listed in a few places (e.g. here: http://www.luatex.org/development.html and in their mailing list announcements).