Added nix-serve config

Could use some work, but it works for now.

modules/services/nix-serve/default.nix

@@ -0,0 +1,52 @@
+{
+  options,
+  config,
+  lib,
+  pkgs,
+  format,
+  ...
+}:
+with lib; let
+  cfg = config.aa.services.nix-serve;
+in {
+  options.aa.services.nix-serve = with types; {
+    enable = mkEnableOption "nix-serve";
+    domain_name = mkOption {
+      type = str;
+      description = "The domain to use.";
+    };
+    subdomain_name = mkOption {
+      type = str;
+      description = "The subdomain to use.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services = {
+      nix-serve = {
+        enable = true;
+        # TODO: Document this or automate the inital creation.
+        secretKeyFile = "/var/gospelCache";
+      };
+
+      nginx = {
+        enable = true;
+        virtualHosts = {
+          "${cfg.subdomain_name}.${cfg.domain_name}" = {
+            serverAliases = [${cfg.subdomain_name}];
+            locations."/".extraConfig = ''
+              proxy_pass http://localhost:${toString config.services.nix-serve.port};
+              proxy_set_header Host $host;
+              proxy_set_header X-Real-IP $remote_addr;
+              proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            '';
+          };
+        };
+      };
+    };
+
+    networking.firewall = {
+      allowedTCPPorts = [80];
+    };
+  };
+}