module: provide option to specify EnvironmentFile for secrets

The systemd service module references the module's environmentFile in a
list to allow for merging with EnvironmentFiles injected elsewhere.

module.nix

@@ -13,6 +13,7 @@ let
     mkMerge;
 
   inherit (lib.options)
+    mdDoc
     mkEnableOption
     mkOption;
 
@@ -45,11 +46,48 @@ in
         type = types.bool;
         default = true;
       };
+
+      environmentFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        example = "/run/secrets/authentik/authentik-env";
+        description = mdDoc ''
+          Environment file as defined in {manpage}`systemd.exec(5)`.
+
+          Secrets may be passed to the service without adding them to the world-readable
+          /nix/store, by specifying the desied secrets as environment variables according
+          to the authentic documentation.
+
+          ```
+            # example content
+            AUTHENTIK_SECRET_KEY=<secret key>
+            AUTHENTIK_EMAIL__PASSWORD=<smtp password>
+          ```
+        '';
+      };
     };
 
     # LDAP oupost
     authentik-ldap = {
       enable = mkEnableOption "authentik LDAP outpost";
+
+      environmentFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        example = "/run/secrets/authentik-ldap/authentik-ldap-env";
+        description = mdDoc ''
+          Environment file as defined in {manpage}`systemd.exec(5)`.
+
+          Secrets may be passed to the service without adding them to the world-readable
+          /nix/store, by specifying the desied secrets as environment variables according
+          to the authentic documentation.
+
+          ```
+            # example content
+            AUTHENTIK_TOKEN=<token from authentik for this outpost>
+          ```
+        '';
+      };
     };
   };
 
@@ -101,6 +139,7 @@ in
             DynamicUser = true;
             User = "authentik";
             ExecStart = "${cfg.authentikComponents.migrate}/bin/migrate.py";
+            EnvironmentFile = mkIf (cfg.environmentFile != null) [ cfg.environmentFile ];
           };
         };
         authentik-worker = {
@@ -114,6 +153,7 @@ in
             User = "authentik";
             # TODO maybe make this configurable
             ExecStart = "${cfg.authentikComponents.celery}/bin/celery -A authentik.root.celery worker -Ofair --max-tasks-per-child=1 --autoscale 3,1 -E -B -s /tmp/celerybeat-schedule -Q authentik,authentik_scheduled,authentik_events";
+            EnvironmentFile = mkIf (cfg.environmentFile != null) [ cfg.environmentFile ];
           };
         };
         authentik = {
@@ -140,6 +180,7 @@ in
             WorkingDirectory = "%S/authentik";
             DynamicUser = true;
             ExecStart = "${cfg.authentikComponents.gopkgs}/bin/server";
+            EnvironmentFile = mkIf (cfg.environmentFile != null) [ cfg.environmentFile ];
           };
         };
       };
@@ -163,6 +204,7 @@ in
           WorkingDirectory = "%t/authentik-ldap";
           DynamicUser = true;
           ExecStart = "${config.services.authentik.authentikComponents.gopkgs}/bin/ldap";
+          EnvironmentFile = mkIf (cfg.environmentFile != null) [ cfg.environmentFile ];
         };
       };
     }))

test.nix

@@ -2,8 +2,10 @@
 , nixosModules
 }:
 let
-  # use a root-owned EnvironmentFile in production instead (systemd.services.<name>.serviceConfig.EnvironmentFile)
+  # use a root-owned EnvironmentFile in production instead (services.authentik.environmentFile)
-  authentiksecret = "thissecretwillbeinthenixstore";
+  authentik-env = pkgs.writeText "authentik-test-secret-env" ''
+    AUTHENTIK_SECRET_KEY=thissecretwillbeinthenixstore
+  '';
 in
 pkgs.nixosTest {
   name = "authentik";
@@ -19,17 +21,10 @@ pkgs.nixosTest {
         "${pkgs.path}/nixos/tests/common/x11.nix"
       ];
 
-      services.authentik.enable = true;
+      services.authentik = {
-
+        enable = true;
-      systemd.services.authentik-migrate.serviceConfig.Environment = [
+        environmentFile = authentik-env;
-        "AUTHENTIK_SECRET_KEY=${authentiksecret}"
+      };
-      ];
-      systemd.services.authentik-worker.serviceConfig.Environment = [
-        "AUTHENTIK_SECRET_KEY=${authentiksecret}"
-      ];
-      systemd.services.authentik.serviceConfig.Environment = [
-        "AUTHENTIK_SECRET_KEY=${authentiksecret}"
-      ];
 
       services.xserver.enable = true;
       test-support.displayManager.auto.user = "alice";