Major config overhaul: use custom modules, setup for multi-host config, and less boilerplate

modules/system/security/sshd/default.nix

@@ -0,0 +1,25 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.systemSettings.security.sshd;
+in {
+  options = {
+    systemSettings.security.sshd = {
+      enable = lib.mkEnableOption "Enable incoming ssh connections";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Enable incoming ssh
+    services.openssh = {
+      enable = true;
+      openFirewall = true;
+      settings = {
+        PasswordAuthentication = false;
+        PermitRootLogin = "no";
+      };
+    };
+    # Don't forget to set:
+    # users.users.${username}.openssh.authorizedKeys.keys = "myAuthorizedKey";
+  };
+}