feat: SMIME signed notification emails

- Add mail interceptor the signs outgoing email with SMIME
- Add lib and helpers to work with SMIME data
- New configuration params for setting up SMIME key and cert files

1 files changed, 46 insertions, 0 deletions

diff --git a/spec/initializers/action_mailer_hooks_spec.rb b/spec/initializers/action_mailer_hooks_spec.rb
new file mode 100644
index 00000000000..3826ed9b00a
--- /dev/null
+++ b/spec/initializers/action_mailer_hooks_spec.rb
@@ -0,0 +1,46 @@
+require 'spec_helper'
+
+describe 'ActionMailer hooks' do
+  describe 'smime signature interceptor' do
+    before do
+      class_spy(ActionMailer::Base).as_stubbed_const
+    end
+
+    it 'is disabled by default' do
+      load Rails.root.join('config/initializers/action_mailer_hooks.rb')
+
+      expect(ActionMailer::Base).not_to(
+        have_received(:register_interceptor).with(Gitlab::Email::Hook::SmimeSignatureInterceptor))
+    end
+
+    describe 'interceptor testbed' do
+      where(:email_enabled, :email_smime_enabled, :smime_interceptor_enabled) do
+        [
+          [false, false, false],
+          [false, true,  false],
+          [true,  false, false],
+          [true,  true,  true]
+        ]
+      end
+
+      with_them do
+        before do
+          stub_config_setting(email_enabled: email_enabled)
+          stub_config_setting(email_smime: { enabled: email_smime_enabled })
+        end
+
+        it 'is enabled depending on settings' do
+          load Rails.root.join('config/initializers/action_mailer_hooks.rb')
+
+          if smime_interceptor_enabled
+            expect(ActionMailer::Base).to(
+              have_received(:register_interceptor).with(Gitlab::Email::Hook::SmimeSignatureInterceptor))
+          else
+            expect(ActionMailer::Base).not_to(
+              have_received(:register_interceptor).with(Gitlab::Email::Hook::SmimeSignatureInterceptor))
+          end
+        end
+      end
+    end
+  end
+end