systemd user unit to set SSH_AUTH_SOCK variable for X11/Wayland/GNOME and make it work with GnuPG agent

ssh-auth-sock.service

# Place this file in ~/.config/systemd/user/ssh-auth-sock.service
# $ systemctl --user daemon-reload
# $ systemctl --user enable --now ssh-auth-sock.service
# Add 'echo UPDATESTARTUPTTY | gpg-connect-agent >/dev/null' in your ~/.bashrc.
# Logout or reboot.

[Unit]
Description=Set SSH_AUTH_SOCK to GnuPG agent

[Service]
Type=oneshot

# disable gnome-keyring-ssh
ExecStartPre=/bin/bash -c 'cat /etc/xdg/autostart/gnome-keyring-ssh.desktop \
  <(echo "Hidden=true") > %h/.config/autostart/gnome-keyring-ssh.desktop'

# set environment
ExecStart=/usr/bin/bash -c 'systemctl --user set-environment \
  SSH_AUTH_SOCK=$(gpgconf --list-dirs agent-ssh-socket) \
  GSM_SKIP_SSH_AGENT_WORKAROUND="true"'

# See the below link for why we need GSM_SKIP_SSH_AGENT_WORKAROUND:
# https://git.gnome.org/browse/gnome-session/tree/gnome-session/main.c?h=3.24.0#n419

[Install]
WantedBy=default.target