```ruby
class LineController < ApplicationController
  def callback
  end
end
```

Add - Add Line callback
user
```ruby
class LineController < ApplicationController
  def callback
    unless Line::Callback.validate_signature? request
      render status: 400, text: 'Bad Request' and return
    else
      Line::Callback.parse request
      render text: "OK" and return
    end
  end
end
```
assistant