postwoman google login doesn't work behind ingress or reverse proxy

Describe the bug
Google login doesn't work when you deploy postwoman behind reverse proxy or ingress

To Reproduce
Steps to reproduce the behavior:
Easiest way to reproduce is run below docker-compose and login to google by http://localhost:80 (reverse_proxy) instead of http://localhost:3000 (postwoman direct)

https://gist.github.com/javad-hajiani/c604f42e3fc0068ae65b482a3adf8278

Expected behavior
google login work properly like what you have already without reverse_proxy

Desktop (please complete the following information):

• OS: ubuntu 18.04
• Browser chromium
• Version 83

[liyasthomas]

Login is disabled for all request URLs except postwoman.io due to security concerns. Kindly use postwoman.io to make use of sync feature.

Duplicate of #817

[schndr]

@liyasthomas Can you please elaborate the security concerns in detail?