From ea4d7e7f4044c84eb78eb260d89958348718fdf6 Mon Sep 17 00:00:00 2001
From: Adrien Dessy <adrien@citizenlab.co>
Date: Wed, 18 Dec 2024 18:01:42 +0100
Subject: [PATCH] [TAN-3184] Configure cookie rotation for SHA1 to SHA256
 migration

---
 back/config/initializers/cookie_rotator.rb | 25 ++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 back/config/initializers/cookie_rotator.rb

diff --git a/back/config/initializers/cookie_rotator.rb b/back/config/initializers/cookie_rotator.rb
new file mode 100644
index 000000000000..1630a937bff4
--- /dev/null
+++ b/back/config/initializers/cookie_rotator.rb
@@ -0,0 +1,25 @@
+# This initializer sets up cookie rotation to ensure a smooth transition from SHA1 to SHA256,
+# which is the hash algorithm used by default by the key generator digest class in Rails 7.0.
+# For more information, refer to the Rails 7.0 upgrade guide:
+# https://guides.rubyonrails.org/upgrading_ruby_on_rails.html#key-generator-digest-class-changing-to-use-sha256
+
+Rails.application.config.after_initialize do
+  Rails.application.config.action_dispatch.cookies_rotations.tap do |cookies|
+    authenticated_encrypted_cookie_salt = Rails.application.config.action_dispatch.authenticated_encrypted_cookie_salt
+    signed_cookie_salt = Rails.application.config.action_dispatch.signed_cookie_salt
+
+    secret_key_base = Rails.application.secret_key_base
+
+    key_generator = ActiveSupport::KeyGenerator.new(
+      secret_key_base, iterations: 1000, hash_digest_class: OpenSSL::Digest::SHA1
+    )
+
+    key_len = ActiveSupport::MessageEncryptor.key_len
+
+    old_encrypted_secret = key_generator.generate_key(authenticated_encrypted_cookie_salt, key_len)
+    old_signed_secret = key_generator.generate_key(signed_cookie_salt)
+
+    cookies.rotate :encrypted, old_encrypted_secret
+    cookies.rotate :signed, old_signed_secret
+  end
+end