nix/nixos/common/services/openssh.nix

{ config, pkgs, hostname, ... }: {
  # By default no ports are open.
  # When ./tailscale.nix is imported, port 22 on the tailscale interface is then opened.
  services.openssh = {
    enable = true;
    # Defaults to true -- I don't like it when services default to true for opening firewalls.
    openFirewall = false;
    settings = {
      LogLevel = "VERBOSE"; # Used for fail2ban monitoring
      PermitRootLogin = "no";
      PasswordAuthentication = false;
    };
    banner = ''
    --
    Welcome to ${hostname}

    You are accessing a U.S. Government (USG) Information 
    System (IS) that is provided for USG-authorized use only.

    By using this IS (which includes any device attached to 
    this IS), you consent to the following conditions:
    
    - The USG routinely intercepts and monitors communications 
      on this IS for purposes including, but not limited 
      to, renetration testing, COMSEC monitoring, network 
      operations and defense, personnel misconduct (PM), law 
      enforcement (LE),  and counterintelligence (CI) 
      investigations.
    
    - At any time, the USG may inspect and seize data stored 
      on this IS.
    
    - Communications using, or data stored on, this IS are not 
      private, are subject to routine monitoring, interception, 
      and search, and may be disclosed or used for any 
      USG-authorized purpose.
    
    - This IS includes security measures (e.g., authentication 
      and access controls) to protect USG interests--not for 
      your personal benefit or privacy.
    
    - Notwithstanding the above, using this IS does not 
      constitute consent to PM, LE or CI investigative 
      searching or monitoring of the content of privileged 
      communications, or work product, elated to personal 
      representation or services by attorneys, psychotherapists, 
      or clergy, and their assistants. Such communications 
      and work product are private and confidential. See User 
      Agreement for details. 

    --
    '';
  };
}