As per the TwitterKit docs:
To create a new Twitter app or use existing Twitter app, visit Twitter apps dashboard and copy the keys from the “Keys and Access Tokens” tab of your app page.
To add call back URL:
In Twitter apps dashboard, find your application and go to the permissions tab.
Select the appropriate permissions for your needs (e.g. “Read and write”)
If you are using login, add a placeholder URL in the Callback URL field (eg. “http://placeholder.com”).
Click update settings.
You can just use http://placeholder.com and that should work fine for redirecting to the Twitter App