diff --git a/modules/accounts/calendar.nix b/modules/accounts/calendar.nix
index 961cd0b3a..bfbc3e124 100644
--- a/modules/accounts/calendar.nix
+++ b/modules/accounts/calendar.nix
@@ -58,15 +58,6 @@ let
         description = "User name for authentication.";
       };
 
-      # userNameCommand = mkOption {
-      #   type = types.nullOr (types.listOf types.str);
-      #   default = null;
-      #   example = [ "~/get-username.sh" ];
-      #   description = ''
-      #     A command that prints the user name to standard output.
-      #   '';
-      # };
-
       passwordCommand = mkOption {
         type = types.nullOr (types.listOf types.str);
         default = null;
diff --git a/modules/programs/vdirsyncer-accounts.nix b/modules/programs/vdirsyncer-accounts.nix
index 4edd17429..7ab9521c1 100644
--- a/modules/programs/vdirsyncer-accounts.nix
+++ b/modules/programs/vdirsyncer-accounts.nix
@@ -10,6 +10,20 @@ in {
   options.vdirsyncer = {
     enable = mkEnableOption "synchronization using vdirsyncer";
 
+    urlCommand = mkOption {
+      type = types.nullOr (types.listOf types.str);
+      default = null;
+      example = [ "~/get-url.sh" ];
+      description = "A command that prints the URL of the storage.";
+    };
+
+    userNameCommand = mkOption {
+      type = types.nullOr (types.listOf types.str);
+      default = null;
+      example = [ "~/get-username.sh" ];
+      description = "A command that prints the user name to standard output.";
+    };
+
     collections = mkOption {
       type = types.nullOr (types.listOf collection);
       default = null;
diff --git a/modules/programs/vdirsyncer.nix b/modules/programs/vdirsyncer.nix
index 32c003394..562d7b4be 100644
--- a/modules/programs/vdirsyncer.nix
+++ b/modules/programs/vdirsyncer.nix
@@ -32,27 +32,25 @@ let
     });
 
   remoteStorage = a:
-    filterAttrs (_: v: v != null) ((getAttrs [
-      "type"
-      "url"
-      "userName"
-      #"userNameCommand"
-      "passwordCommand"
-    ] a.remote) // (if a.vdirsyncer == null then
-      { }
-    else
-      getAttrs [
-        "itemTypes"
-        "verify"
-        "verifyFingerprint"
-        "auth"
-        "authCert"
-        "userAgent"
-        "tokenFile"
-        "clientIdCommand"
-        "clientSecretCommand"
-        "timeRange"
-      ] a.vdirsyncer));
+    filterAttrs (_: v: v != null)
+    ((getAttrs [ "type" "url" "userName" "passwordCommand" ] a.remote)
+      // (if a.vdirsyncer == null then
+        { }
+      else
+        getAttrs [
+          "urlCommand"
+          "userNameCommand"
+          "itemTypes"
+          "verify"
+          "verifyFingerprint"
+          "auth"
+          "authCert"
+          "userAgent"
+          "tokenFile"
+          "clientIdCommand"
+          "clientSecretCommand"
+          "timeRange"
+        ] a.vdirsyncer));
 
   pair = a:
     with a.vdirsyncer;
@@ -77,6 +75,8 @@ let
       ''post_hook = "${v}"''
     else if (n == "url") then
       ''url = "${v}"''
+    else if (n == "urlCommand") then
+      "url.fetch = ${listString (map wrap ([ "command" ] ++ v))}"
     else if (n == "timeRange") then ''
       start_date = "${v.start}"
       end_date = "${v.end}"'' else if (n == "itemTypes") then
@@ -196,6 +196,9 @@ in {
   config = mkIf cfg.enable {
     assertions = let
 
+      mutuallyExclusiveOptions =
+        [ [ "url" "urlCommand" ] [ "userName" "userNameCommand" ] ];
+
       requiredOptions = t:
         if (t == "caldav" || t == "carddav" || t == "http") then
           [ "url" ]
@@ -213,6 +216,7 @@ in {
 
       allowedOptions = let
         remoteOptions = [
+          "urlCommand"
           "userName"
           "userNameCommand"
           "password"
@@ -264,7 +268,16 @@ in {
               Storage ${n} is of type ${v.type}, but required
               option ${a} is not set.
             '';
-          }]) required)) (removeAttrs v [ "type" "_module" ]);
+          }]) required) ++ map (attrs:
+            let
+              defined = attrNames (filterAttrs (n: v: v != null)
+                (genAttrs attrs (a: v.${a} or null)));
+            in {
+              assertion = length defined <= 1;
+              message = "Storage ${n} has mutually exclusive options: ${
+                  concatStringsSep ", " defined
+                }";
+            }) mutuallyExclusiveOptions) (removeAttrs v [ "type" "_module" ]);
 
       storageAssertions = flatten (mapAttrsToList assertStorage localStorages)
         ++ flatten (mapAttrsToList assertStorage remoteStorages);