restrict remote users from indexing

lib/pleroma/web/metadata.ex

@@ -6,7 +6,12 @@ defmodule Pleroma.Web.Metadata do
   alias Phoenix.HTML
 
   def build_tags(params) do
-    Enum.reduce(Pleroma.Config.get([__MODULE__, :providers], []), "", fn parser, acc ->
+    providers = [
+      Pleroma.Web.Metadata.Providers.RestrictIndexing
+      | Pleroma.Config.get([__MODULE__, :providers], [])
+    ]
+
+    Enum.reduce(providers, "", fn parser, acc ->
       rendered_html =
         params
         |> parser.build_tags()

lib/pleroma/web/metadata/restrict_indexing.ex

@@ -0,0 +1,25 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Metadata.Providers.RestrictIndexing do
+  @behaviour Pleroma.Web.Metadata.Providers.Provider
+
+  @moduledoc """
+  Restricts indexing of remote users.
+  """
+
+  @impl true
+  def build_tags(%{user: %{local: false}}) do
+    [
+      {:meta,
+       [
+         name: "robots",
+         content: "noindex, noarchive"
+       ], []}
+    ]
+  end
+
+  @impl true
+  def build_tags(%{user: %{local: true}}), do: []
+end