How to get Http-proxy-middleware to work with firebase cloud functions?

Question

currently I am creating an API Gateway and for that I started working with the http-proxy-middleware library.
However I have read from the docs that libraries which modify the request usually cause problems with http-proxy-middleware (e.g body parser).
I reckon that the Firebase Cloud Functions library does that as well.
Has somebody experienced the same?
For Example, a post request with body does not terminate until a timeout is triggered.
And I am pretty much sure, that the problem cause is the Firebase library, simply because whenever I comment it out, the post request works normally.