fix(mailer): make Mua trust the CAStore bundle

Mua (the SMTP adapter in the docs) trusts the OS CA store unless it gets
a CA. Pass the CAStore bundle, but keep a CA that the admin set.

test/pleroma/emails/mailer_test.exs

@@ -61,4 +61,33 @@ defmodule Pleroma.Emails.MailerTest do
     assert hackney_options[:ssl_options] ==
              Pleroma.HTTP.TLS.ssl_options()
   end
+
+  describe "put_mua_cacertfile/1" do
+    test "makes Mua trust the CAStore bundle" do
+      config = Mailer.put_mua_cacertfile(adapter: Swoosh.Adapters.Mua, relay: "mail.example.com")
+
+      assert config[:ssl] == [cacertfile: CAStore.file_path()]
+      assert config[:relay] == "mail.example.com"
+    end
+
+    test "keeps other ssl options" do
+      config = Mailer.put_mua_cacertfile(adapter: Swoosh.Adapters.Mua, ssl: [depth: 3])
+
+      assert config[:ssl] == [cacertfile: CAStore.file_path(), depth: 3]
+    end
+
+    test "keeps a CA that the admin set" do
+      config = [adapter: Swoosh.Adapters.Mua, ssl: [cacertfile: "/etc/ssl/smtp.pem"]]
+      assert Mailer.put_mua_cacertfile(config) == config
+
+      config = [adapter: Swoosh.Adapters.Mua, ssl: [cacerts: []]]
+      assert Mailer.put_mua_cacertfile(config) == config
+    end
+
+    test "leaves other adapters alone" do
+      config = [adapter: Swoosh.Adapters.SMTP, relay: "mail.example.com"]
+
+      assert Mailer.put_mua_cacertfile(config) == config
+    end
+  end
 end