Overview

1. Install Web Greeter 3.0beta4
2. Enable web-greeter in /etc/lightdm/lightdm.conf
3. Reboot your system (or manually restart lightdm).

Install Web Greeter 3.0beta4

Use Distro Package Manager

Distro	Install Command/Links
	sudo pacman -S web-greeter-next
	sudo pacman -S web-greeter-next [*]
	dnf copr enable antergos/web-greeter && dnf install web-greeter
	1 Click Install
	PPA

[*]: Antergos repo must be added to your pacman.conf

From Source

sudo pip install whither
git clone https://github.com/antergos/web-greeter.git
cd web-greeter
make install

Enable web-greeter in /etc/lightdm/lightdm.conf

greeter-session=web-greeter