fix(http): keep the configured TLS options with Gun

[:http, :adapter, :ssl_options] is Hackney's key, and AdminFE sets it.
Gun reads tls_opts, so with Gun as the default these settings were lost
without a warning. Use them as tls_opts unless tls_opts is set.

lib/pleroma/http/adapter_helper/gun.ex

@@ -28,6 +28,7 @@ defmodule Pleroma.HTTP.AdapterHelper.Gun do
 
     @defaults
     |> Keyword.merge(config_opts)
+    |> ssl_options_to_tls_opts()
     |> add_scheme_opts(uri)
     |> AdapterHelper.maybe_add_proxy(proxy)
     |> Keyword.merge(incoming_opts)
@@ -35,6 +36,15 @@ defmodule Pleroma.HTTP.AdapterHelper.Gun do
     |> maybe_stream()
   end
 
+  # [:http, :adapter, :ssl_options] is Hackney's name for the TLS options,
+  # and AdminFE sets it. Keep those settings when Gun is the adapter.
+  defp ssl_options_to_tls_opts(opts) do
+    case Keyword.pop(opts, :ssl_options) do
+      {nil, opts} -> opts
+      {ssl_options, opts} -> Keyword.put_new(opts, :tls_opts, ssl_options)
+    end
+  end
+
   defp add_scheme_opts(opts, %{scheme: "http"}), do: opts
 
   defp add_scheme_opts(opts, %{scheme: "https"}) do

test/pleroma/http/adapter_helper/gun_test.exs

@@ -50,6 +50,15 @@ defmodule Pleroma.HTTP.AdapterHelper.GunTest do
       assert Keyword.has_key?(defaults, :b)
     end
 
+    test "uses Hackney's ssl_options from the config as Gun's tls_opts" do
+      clear_config([:http, :adapter], ssl_options: [versions: [:"tlsv1.3"]])
+
+      opts = Gun.options([], URI.parse("https://example.com"))
+
+      assert opts[:tls_opts] == [versions: [:"tlsv1.3"]]
+      refute Keyword.has_key?(opts, :ssl_options)
+    end
+
     test "parses string proxy host & port" do
       clear_config([:http, :proxy_url], "localhost:8123")