Add borg server module

modules/borg-server.nix

@@ -0,0 +1,172 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.borgbackup-server;
+in
+
+{
+  options.services.borgbackup-server = {
+    enable = mkEnableOption "Borg backup server";
+
+    dataDir = mkOption {
+      type = types.str;
+      default = "/srv/borg";
+      example = "/mnt/backup/borg";
+      description = "Base directory for all borg repositories";
+    };
+
+    users = mkOption {
+      type = types.attrsOf (types.submodule {
+        options = {
+          publicKeys = mkOption {
+            type = types.listOf types.str;
+            example = [ "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGxyz..." ];
+            description = "List of SSH public keys for this user";
+          };
+        };
+      });
+      default = {};
+      example = {
+        alice = {
+          publicKeys = [ "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGxyz..." ];
+        };
+      };
+      description = "Borg backup users configuration";
+    };
+
+    sshPort = mkOption {
+      type = types.port;
+      default = 22;
+      example = 2222;
+      description = "SSH port for borg connections";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # Install required packages
+    environment.systemPackages = [ pkgs.borgbackup pkgs.openssh ];
+
+    # Create borg-server group
+    users.groups.borg-server = {};
+
+    # Create a system user for each borg user
+    users.users = mapAttrs (username: userCfg: {
+      isSystemUser = true;
+      group = "borg-server";
+      home = "${cfg.dataDir}/${username}";
+      createHome = true;
+      shell = pkgs.bash;
+      description = "Borg backup user ${username}";
+      openssh.authorizedKeys.keys = map (key: 
+        "command=\"borg serve --restrict-to-path ${cfg.dataDir}/${username}\",restrict ${key}"
+      ) userCfg.publicKeys;
+    }) cfg.users;
+
+    # Ensure proper permissions on data directory
+    systemd.tmpfiles.rules = [
+      "d ${cfg.dataDir} 0755 root borg-server -"
+    ] ++ (mapAttrsToList (username: _: 
+      "d ${cfg.dataDir}/${username} 0700 ${username} borg-server -"
+    ) cfg.users);
+
+    # Configure SSH for borg access
+    services.openssh = {
+      enable = true;
+      ports = [ cfg.sshPort ];
+      settings = {
+        # SSH hardening for borg users
+        Match = "Group borg-server";
+        PasswordAuthentication = false;
+        PubkeyAuthentication = true;
+        PermitRootLogin = "no";
+        X11Forwarding = false;
+        AllowAgentForwarding = false;
+        AllowTcpForwarding = false;
+        PermitTunnel = "no";
+        
+        # Keep connection alive settings
+        ClientAliveInterval = 10;
+        ClientAliveCountMax = 30;
+      };
+    };
+
+    # Open firewall port
+    networking.firewall.allowedTCPPorts = mkIf (cfg.sshPort != 22) [ cfg.sshPort ];
+
+    # Create convenience scripts and aliases
+    environment.shellAliases = {
+      borg-server-status = "systemctl status sshd";
+      borg-server-users = "ls -la ${cfg.dataDir}";
+      borg-server-logs = "journalctl -u sshd -f";
+    };
+
+    # Create a helper script for adding new users
+    environment.etc."borg-server/add-user.sh" = {
+      text = ''
+        set -e
+        
+        if [ $# -lt 2 ]; then
+          echo "Usage: $0 <username> <ssh-public-key>"
+          echo "Example: $0 alice 'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGxyz...'"
+          exit 1
+        fi
+        
+        USERNAME="$1"
+        SSH_KEY="$2"
+        USER_DIR="${cfg.dataDir}/$USERNAME"
+        
+        echo "To add user '$USERNAME', add the following to your NixOS configuration:"
+        echo ""
+        echo "services.borgbackup-server.users.$USERNAME = {"
+        echo "  publicKeys = [ \"$SSH_KEY\" ];"
+        echo "};"
+        echo ""
+        echo "Then rebuild your system with: nixos-rebuild switch"
+      '';
+      mode = "0755";
+    };
+
+    # Create a helper script for checking repository info
+    environment.etc."borg-server/check-repo.sh" = {
+      text = ''
+        set -e
+        
+        if [ $# -lt 1 ]; then
+          echo "Usage: $0 <username> [repository]"
+          echo "Example: $0 alice"
+          echo "Example: $0 alice main-repo"
+          exit 1
+        fi
+        
+        USERNAME="$1"
+        REPO_NAME="''${2:-}"
+        USER_DIR="${cfg.dataDir}/$USERNAME"
+        
+        if [ ! -d "$USER_DIR" ]; then
+          echo "User directory $USER_DIR does not exist"
+          exit 1
+        fi
+        
+        if [ -n "$REPO_NAME" ]; then
+          REPO_PATH="$USER_DIR/$REPO_NAME"
+        else
+          echo "Repositories for user $USERNAME:"
+          ls -la "$USER_DIR"
+          exit 0
+        fi
+        
+        if [ -d "$REPO_PATH" ]; then
+          echo "Repository info for $USERNAME/$REPO_NAME:"
+          sudo -u "$USERNAME" borg info "$REPO_PATH"
+        else
+          echo "Repository $REPO_PATH does not exist"
+          exit 1
+        fi
+      '';
+      mode = "0755";
+    };
+
+  };
+}