nixos: add nginx-sso service

nixos/modules/module-list.nix

@@ -681,6 +681,7 @@
   ./services/security/hologram-server.nix
   ./services/security/hologram-agent.nix
   ./services/security/munge.nix
+  ./services/security/nginx-sso.nix
   ./services/security/oauth2_proxy.nix
   ./services/security/oauth2_proxy_nginx.nix
   ./services/security/physlock.nix

nixos/modules/services/security/nginx-sso.nix

@@ -0,0 +1,58 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.nginx.sso;
+  pkg = getBin pkgs.nginx-sso;
+  configYml = pkgs.writeText "nginx-sso.yml" (builtins.toJSON cfg.configuration);
+in {
+  options.services.nginx.sso = {
+    enable = mkEnableOption "nginx-sso service";
+
+    configuration = mkOption {
+      type = types.attrsOf types.unspecified;
+      default = {};
+      example = literalExample ''
+        {
+          listen = { addr = "127.0.0.1"; port = 8080; };
+
+          providers.token.tokens = {
+            myuser = "MyToken";
+          };
+
+          acl = {
+            rule_sets = [
+              {
+                rules = [ { field = "x-application"; equals = "MyApp"; } ];
+                allow = [ "myuser" ];
+              }
+            ];
+          };
+        }
+      '';
+      description = ''
+        nginx-sso configuration
+        (<link xlink:href="https://github.com/Luzifer/nginx-sso/wiki/Main-Configuration">documentation</link>)
+        as a Nix attribute set.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.nginx-sso = {
+      description = "Nginx SSO Backend";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        ExecStart = ''
+          ${pkg}/bin/nginx-sso \
+            --config ${configYml} \
+            --frontend-dir ${pkg}/share/frontend
+        '';
+        Restart = "always";
+        DynamicUser = true;
+      };
+    };
+  };
+}