This is a middleware service, built for ctms-plus. This service does not store, or collect data from request or response. You can verify this by reading the sourcecode of this project.
For someone saying that the deployed code is modified to collect data, this repo is directly deployed onto heroku, which mean it is impossible to modify, or inject new code in the deployment process unless we change it directly on github. (TLDR: source code on heroku is the same with this repo).
For an alternative version written in PHP, see ctms-plus-middleware.