Ali Ahmadi has provided SlackBuilds for lightdm and its greeter since several years, now in his
GitHub repository. I ship
lightdm, l
ightm-gtk-greeter and
lightm-gtk-greeter-settings packages in Slint, built using his SlackBuilds with some adaptation, so that lightdm be accessible with speech using Orca. I have also include a PAM package in Slint, only because it's needed by lightdm. Ali is also a SlackBuild contributor for some software related (not surprisingly) to Indonesian language.
A also ship
gdm-2.20.11 in Slint, fully accessible with braille and speech. As old as be this version, it still builds and run on Slackware64-current, so I intend to continue shipping it in Slint 15.