1 files changed, 50 insertions, 0 deletions
diff --git a/lib/gitlab/email/hook/smime_signature_interceptor.rb b/lib/gitlab/email/hook/smime_signature_interceptor.rb
new file mode 100644
index 00000000000..e48041d9218
--- /dev/null
+++ b/lib/gitlab/email/hook/smime_signature_interceptor.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Email
+    module Hook
+      class SmimeSignatureInterceptor
+        # Sign emails with SMIME if enabled
+        class << self
+          def delivering_email(message)
+            signed_message = Gitlab::Email::Smime::Signer.sign(
+              cert: certificate.cert,
+              key: certificate.key,
+              data: message.encoded)
+            signed_email = Mail.new(signed_message)
+
+            overwrite_body(message, signed_email)
+            overwrite_headers(message, signed_email)
+          end
+
+          private
+
+          def certificate
+            @certificate ||= Gitlab::Email::Smime::Certificate.from_files(key_path, cert_path)
+          end
+
+          def key_path
+            Gitlab.config.gitlab.email_smime.key_file
+          end
+
+          def cert_path
+            Gitlab.config.gitlab.email_smime.cert_file
+          end
+
+          def overwrite_body(message, signed_email)
+            # since this is a multipart email, assignment to nil is important,
+            # otherwise Message#body will add a new mail part
+            message.body = nil
+            message.body = signed_email.body.encoded
+          end
+
+          def overwrite_headers(message, signed_email)
+            message.content_disposition = signed_email.content_disposition
+            message.content_transfer_encoding = signed_email.content_transfer_encoding
+            message.content_type = signed_email.content_type
+          end
+        end
+      end
+    end
+  end
+end