SDDM

Simple Desktop Display Manager (SDDM) is a display manager supports X11 and Wayland.

Emerge
Install :

Without systemd
If you see performance issues, it might help to add the sddm user to the video group.

Configuration
The configuration file for SDDM is:

Boot service
To start SDDM on boot:

To start SDDM now:

Plasma
Graphical configuration is integrated in Plasma 5 system settings by installing :

Without systemd
Add xdm to your default runlevel and set

After logging in to the X session via sddm, it is a good idea to verify that ConsoleKit is working as intended. By typing ck-list-sessions all active sessions can be listed. The list should include your session, typically running on x11-display-device = '/dev/tty7'. This session should also read active = TRUE. Active being FALSE indicates an issue.

As a fix you can try editing and removing the nox11 from the line mentioning pam_ck_connector.so: