documentation/docs/gentoo-desktop-setup/graphical-session/session-manager.md

Session management is necessary for tracking and giving rights to certain users. For a functional setup install both elogind and turnstile and enable their corresponding services.

root@host:~# emerge -av elogind turnstile
root@host:~# rc-update add elogind boot
root@host:~# rc-update add turnstiled

Then configure pam to allow them to track the user:

...
session optional    pam_elogind.so
session optional    pam_turnstile.so

When a user logs in it should now be able to start a graphical session. This should be done with:

user@host:~$ dbus-run-session -- <window_manager>