niksos/modules/services/ssh.nix

{
    config,
    lib,
    pkgs,
    ...
}: let
    cfg = config.myOptions.services.ssh;

    inherit (lib) getExe' mkEnableOption mkIf mkMerge mkOption;
    inherit (lib.types) attrsOf bool nullOr number str submodule;
    inherit (lib.strings) concatStrings;
    inherit (lib.attrsets) mapAttrsToList;

    ksshaskpass = getExe' pkgs.libsForQt5.ksshaskpass "ksshaskpass";
    ssh-agent = getExe' pkgs.openssh "ssh-agent";
in {
    options.myOptions.services.ssh = {
        daemon = mkOption {
            description = "sshd options";
            type = submodule {
                options = {
                    enable = mkEnableOption "sshd";
                    passwordAuth = mkOption {
                        description = "allow password auth";
                        default = false;
                        type = bool;
                    };
                    allowRoot = mkOption {
                        description = "allow root login";
                        default = false;
                        type = bool;
                    };
                };
            };
        };
        agent = mkOption {
            description = "ssh agent options";
            type = submodule {
                options = {
                    enable = mkEnableOption "ssh-agent";
                    hostAliases = mkOption {
                        description = "host aliases";
                        type = attrsOf (submodule {
                            options = {
                                hostName = mkOption {
                                    description = "hostname to ssh into";
                                    type = str;
                                };
                                port = mkOption {
                                    description = "port to ssh into";
                                    type = nullOr number;
                                    default = null;
                                };
                                user = mkOption {
                                    description = "ssh user";
                                    type = str;
                                    default = "git";
                                };
                                publicKey = mkOption {
                                    description = "public key used for picking the correct key from the ssh-agent";
                                    type = nullOr str;
                                    default = null;
                                };
                            };
                        });
                        default = {};
                    };
                };
            };
        };
    };

    config = mkMerge [
        (mkIf cfg.daemon.enable {
            services.openssh = {
                enable = true;
                settings = {
                    PasswordAuthentication = false;
                    PermitRootLogin = "no";
                    LoginGraceTime = 0;
                };
            };
        })
        (mkIf cfg.agent.enable {
            programs.ssh = {
                enableAskPassword = true;
                askPassword = ksshaskpass;
                extraConfig = ''
                    AddKeysToAgent yes

                    ${concatStrings (mapAttrsToList (name: value: ''
                        Host ${name}
                            HostName        ${value.hostName}
                            User            ${value.user}
                            ${
                                if value.port != null then
                                    "Port            ${toString value.port}"
                                    else ""
                            }
                            ${
                                if value.publicKey != null then
                                    "IdentityFile    ${pkgs.writeText "${name}.pub" value.publicKey}"
                                    else ""
                            }
                    '') cfg.agent.hostAliases)}
                '';
            };

            systemd.user.services.ssh-agent = {
                enable = true;
                description = "SSH key agent";
                serviceConfig = {
                    Type = "simple";
                    ExecStart = "${ssh-agent} -D -a $SSH_AUTH_SOCK";
                };
                environment = {
                    SSH_AUTH_SOCK = "%t/ssh-agent.socket";
                    DISPLAY = ":0";
                };
                wantedBy = [ "default.target" ];
            };

            environment.sessionVariables = {
                SSH_AUTH_SOCK = "\$XDG_RUNTIME_DIR/ssh-agent.socket";
            };
        })
    ];
}