```ruby
# frozen_string_literal: true

module LetterOpenerWeb
  class ApplicationController < ActionController::Base
  end
end
```

Add Rails' built-in CSRF protection
user
```ruby
# frozen_string_literal: true

module LetterOpenerWeb
  class ApplicationController < ActionController::Base
    protect_from_forgery with: :exception
  end
end
```
assistant