Steps to reproduce (tested with Node 8.12.0 and 11.7.0):

git clone https://github.com/buu700/simple-reverse-proxy
cd simple-reverse-proxy
npm install
npm start &
curl -H 'Host: cyph.com' http://localhost/wp-content/uploads/2018/10/auditconclusion.txt

Expected result: Prints content of https://www.cyph.com/wp-content/uploads/2018/10/auditconclusion.txt

Actual result: FetchError: maximum redirect reached at: https://www.cyph.com/wp-content/uploads/2018/10/auditconclusion.txt

Note that it works as expected when changing either the Host header to www.cyph.com or the origin to https://localhost (or both); it's only when redirecting from http://cyph.com -> https://cyph.com -> https://www.cyph.com that the failure occurs.