dotfiles/modules/nixos/services/sshd.nix

{ config, lib, ... }: {

  options = {
    publicKey = lib.mkOption {
      type = lib.types.nullOr lib.types.str;
      description = "Public SSH key authorized for this system.";
      default = null;
    };
    permitRootLogin = lib.mkOption {
      type = lib.types.str;
      description = "Root login settings.";
      default = "no";
    };
  };

  config = lib.mkIf config.services.openssh.enable {
    services.openssh = {
      ports = [ 22 ];
      allowSFTP = true;
      settings = {
        GatewayPorts = "no";
        X11Forwarding = false;
        PasswordAuthentication = false;
        PermitRootLogin = config.permitRootLogin;
      };
    };

    users.users.${config.user}.openssh.authorizedKeys.keys =
      lib.mkIf (config.publicKey != null) [ config.publicKey ];

    # Implement a simple fail2ban service for sshd
    services.sshguard.enable = true;

    # Add terminfo for SSH from popular terminal emulators
    environment.enableAllTerminfo = true;
  };

}