Patch away a deprecation warning caused by Devise

config/initializers/devise.rb

@@ -325,3 +325,10 @@ Devise.setup do |config|
   # changed. Defaults to true, so a user is signed in automatically after changing a password.
   # config.sign_in_after_change_password = true
 end
+
+# https://github.com/heartcombo/devise/issues/5644
+class Devise::SecretKeyFinder
+  def find
+    @application.secret_key_base
+  end
+end