rpi4: add some options for authelia (wip)

hosts/rpi4/authelia.nix

@@ -1,22 +1,89 @@
 { config, lib, pkgs, ... }:
+let
+  inherit (lib) types;
+  inherit (builtins) isNull;
+
+  getUpstreamFromInstance = instance: let
+    inherit (config.services.authelia.instances.${instance}.settings) server;
+    inherit (server) port;
+    host = if server.host == "0.0.0.0" then "127.0.0.1"
+      else if lib.hasInfix ":" server.host then
+        throw "TODO IPv6 not supported in Authelia server address (hard to parse, can't tell if it is [::])."
+      else server.host;
+  in "http://${host}:${port}";
+in
 {
   # authelia
   options.services.nginx = let
-    inherit (lib) types;
     mkAttrsOfSubmoduleOpt = module: lib.mkOption { type = with types; attrsOf (submodule module); };
 
     # make system config accessible from submodules
     systemConfig = config;
 
     # submodule definitions
-    locationModule' = vhostAttrs: { name, config, ... }: {
-    };
     vhostModule = { name, config, ... }@attrs: {
-      options.locations = mkAttrsOfSubmoduleOpt (locationModule' attrs);
+      options = {
+        locations = mkAttrsOfSubmoduleOpt (locationModule' attrs);
+        authelia = {
+          endpoint = {
+            instance = lib.mkOption {
+              description = ''
+                Local Authelia instance to act as the authentication endpoint.
+                This virtualHost will be configured to provide the
+                public-facing authentication service.
+              '';
+              type = with types; nullOr str;
+              default = null;
+            };
+            upstream = lib.mkOption {
+              description = ''
+                Internal URL of the Authelia endpoint to forward authentication
+                requests to.
+              '';
+              type = with types; nullOr str;
+              default = null;
+            };
+          };
+          instance = lib.mkOption {
+            description = ''
+              Local Authelia instance to use. Setting this option will
+              automatically configure Authelia on the specified virtualHost
+              with the given instance of Authelia.
+            '';
+            type = with types; nullOr str;
+            default = null;
+          };
+          upstream = lib.mkOption {
+            description = ''
+              Internal URL of the Authelia endpoint to forward authorization
+              requests to. This should not be the public-facing authentication
+              endpoint URL.
+            '';
+          };
+        };
+      };
+      config = {
+        authelia.upstream = lib.mkIf (!(isNull config.authelia.instance))
+          (getUpstreamFromInstance config.authelia.instance);
+        authelia.endpoint.upstream = lib.mkIf (!(isNull config.authelia.endpoint.instance))
+          (getUpstreamFromInstance config.authelia.endpoint.instance);
+      };
+    };
+
+    locationModule' = vhostAttrs: { name, config, ... }: let
+      vhostConfig = vhostAttrs.config;
+    in {
     };
 
   in {
     virtualHosts = mkAttrsOfSubmoduleOpt vhostModule;
   };
 
+  # TODO check if any vhosts have authelia configured
+  config = lib.mkIf false {
+
+    assertions = [
+      # TODO vhost cannot be both auth endpoint and regular reverse proxy
+    ];
+  };
 }