nixos/mosquitto: add passwordFile and hashedPasswordFile options

nixos/modules/services/networking/mosquitto.nix

@@ -123,12 +123,33 @@ in
               '';
             };
 
+            passwordFile = mkOption {
+              type = with types; uniq (nullOr str);
+              example = "/path/to/file";
+              default = null;
+              description = ''
+                Specifies the path to a file containing the
+                clear text password for the MQTT user.
+              '';
+            };
+
             hashedPassword = mkOption {
               type = with types; uniq (nullOr str);
               default = null;
               description = ''
                 Specifies the hashed password for the MQTT User.
-                <option>hashedPassword</option> overrides <option>password</option>.
+                To generate hashed password install <literal>mosquitto</literal>
+                package and use <literal>mosquitto_passwd</literal>.
+              '';
+            };
+
+            hashedPasswordFile = mkOption {
+              type = with types; uniq (nullOr str);
+              example = "/path/to/file";
+              default = null;
+              description = ''
+                Specifies the path to a file containing the
+                hashed password for the MQTT user.
                 To generate hashed password install <literal>mosquitto</literal>
                 package and use <literal>mosquitto_passwd</literal>.
               '';
@@ -190,6 +211,13 @@ in
 
   config = mkIf cfg.enable {
 
+    assertions = mapAttrsToList (name: cfg: {
+      assertion = length (filter (s: s != null) (with cfg; [
+        password passwordFile hashedPassword hashedPasswordFile
+      ])) <= 1;
+      message = "Cannot set more than one password option";
+    }) cfg.users;
+
     systemd.services.mosquitto = {
       description = "Mosquitto MQTT Broker Daemon";
       wantedBy = [ "multi-user.target" ];
@@ -210,7 +238,11 @@ in
         touch ${cfg.dataDir}/passwd
       '' + concatStringsSep "\n" (
         mapAttrsToList (n: c:
-          if c.hashedPassword != null then
+          if c.hashedPasswordFile != null then
+            "echo '${n}:'$(cat '${c.hashedPasswordFile}') >> ${cfg.dataDir}/passwd"
+          else if c.passwordFile != null then
+            "${pkgs.mosquitto}/bin/mosquitto_passwd -b ${cfg.dataDir}/passwd ${n} $(cat '${c.passwordFile}')"
+          else if c.hashedPassword != null then
             "echo '${n}:${c.hashedPassword}' >> ${cfg.dataDir}/passwd"
           else optionalString (c.password != null)
             "${pkgs.mosquitto}/bin/mosquitto_passwd -b ${cfg.dataDir}/passwd ${n} '${c.password}'"