If you use startx to start X instead of a login manager like gdm/kdm,
you can set the XSESSION variable to anything in /etc/X11/Sessions/ or
any executable. When you run startx, it will run this as the login session.
You can set this in a file in /etc/env.d/ for the entire system,
or set it per-user in ~/.bash_profile (or similar for other shells).
Here's an example of setting it for the whole system:
    echo XSESSION=\
    env-update && source /etc/profile
Starting with ${CATEGORY}/${PN}-1.4.1 serverauth files are no longer kept in the
home directory but rather are created in \$TMPDIR (typically /tmp).  The change
is transparent for most of users, however those that use runtime temporary
directories cleaning tools, like app-admin/tmpreaper, may need to adjust them
not to remove the 'serverauth.*' files.