Tap-to-Click at login screen for principle of least astonishment (POLA)

I've observed many end-users who are confused by the lack of ability to "Tap-to-Click" on their touchpads at the login screen after boot(and screen-lock?). Most---if not all, of these users are migrating from MS Windows or another system which does _not_ prevent this technique.

In accord with the old axiom:

“You Never Get A Second Chance to Make a First Impression” – Will Rogers

Let's not let this be the first negative experience that converts and first-timers run into!

Tap-to-click on touchpads is enabled and works normally during the Ubiquity installer.

I'm not sure if libinput is to blame, but I do notice that I frequently have to enable the tap-to-click function in gnome-settings after first login.

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: gdm3 3.30.1-1ubuntu5
ProcVersionSignature: Ubuntu 4.18.0-12.13-generic 4.18.17
Uname: Linux 4.18.0-12-generic x86_64
ApportVersion: 2.20.10-0ubuntu13.1
Architecture: amd64
Date: Sat Dec 15 09:12:01 2018
InstallationDate: Installed on 2018-11-08 (37 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gdm3
UpgradeStatus: No upgrade log present (probably fresh install)