Allow specifying custom envs and secrets for providers

lib/modules/rclone.nix

@@ -1,8 +1,17 @@
 { config, lib, pkgs, ... }:
 let
+  mkProvider =
+    { secretLoader ? ({ ... }: ""), envLoader ? ({ ... }: { }), options ? {}, ... }: {
+      inherit
+        secretLoader
+        envLoader
+        options
+      ;
+    };
+
   syncProviders = {
-    nextcloud = {};
-    proton = {};
+    nextcloud = mkProvider {};
+    proton = mkProvider {};
   };
 
   syncType = lib.types.submodule (
@@ -39,6 +48,11 @@ let
           default = [];
         };
       };
+
+      config = {
+        environment = syncProviders.${config.type}.envLoader config;
+        secretsScript = syncProviders.${config.type}.secretLoader config;
+      };
     });
 in {
   options = {
@@ -89,7 +103,34 @@ in {
                   (lib.getExe script);
             };
           };
-        };
+        } // (
+          lib.attrsets.concatMapAttrs
+          (name: sync:
+            let
+              serviceName = "rclone-sync-${name}";
+            in {
+              ${serviceName} = {
+                Unit = {
+                  Description = "${sync.type}";
+                };
+
+                Service = {
+                  Environment = lib.mapAttrsToList
+                    (key: val: (lib.escapeShellArg "${key}=${val}"))
+                    sync.environment;
+
+                  ExecStart =
+                    let
+                      script = pkgs.writeShellScriptBin serviceName ''
+                        ${sync.secretsScript}
+                        bash -c echo hello world
+                      '';
+                    in
+                      (lib.getExe script);
+                };
+              };
+            })
+          cfg.configs);
 
         targets.rclone = {
           Unit = {