VPNs for China recommendation(Try this first): http://startuplivingchina.com/best-vpn-for-china/
List of tools circumcising GFW in Chinese: https://wsgzao.github.io/post/fq/
Backup plan(Google service with public account, do not enter personal info, but you can setup your own account, only Chinese documentation is available): https://github.com/XX-net/XX-Net/wiki/English-Home-Page
Check out XX-Net https://github.com/XX-net/XX-Net A very handy proxy created base on Google App Engine. It's preloaded with public accounts, works out of box. nonetheless deploy your own account by following the tutorial, so others don't see your data. Good luck.
I already have a tiny server on GCP. I would like to launch there a web proxy, maybe in a docker.
Github gives me this thing https://github.com/XX-net/XX-Net but it's Chinese and Python while I need English doc and C/C++/Go/anything_just_binary.
Google gives me this thing https://github.com/tinyproxy/tinyproxy -- maybe it's the best, idk. I don't need features-rich solution, I only need to do HEAD/GET requests (probably with oauth headers) to pages and images on tumblr.