{ pkgs, ... }:
{
  # GPG.
  services.udev.packages = [ pkgs.yubikey-personalization ];

  programs.gnupg.agent = {
    enable = true;
    enableSSHSupport = true;
    pinentryPackage = pkgs.pinentry-tty;
  };

  # PCSC.
  services.pcscd.enable = true;

  # Yubikey touch notification.
  # ISSUE: Not working on Sway with Mako for some reason.
  programs.yubikey-touch-detector.enable = true;

  environment.systemPackages = with pkgs; [
    libfido2
    yubikey-manager
    # yubioath-desktop # OTP.
  ];

  # Store GPG data on tmpfs.
  # environment.variables = {
  #   GNUPGHOME = "$(mktemp -d -t gnupg-$(date +%Y-%m-%d)-XXXXXXXXXX)";
  # };
}