adhoc query form doesn't work with reverse proxy

[riznob]

I am using nginx as a reverse proxy to host phppgadmin at a different context root, /phppgadmin/. The form to run an adhoc query has an action="/display.php". This leads to a 404 because the form action does not represent the path needed due to the reverse proxy.

Steps to reproduce:
Download the attached docker-compose.yml.txt and nginx.conf.txt files to a common directory.
Rename each file, removing the .txt extension.
Run docker-compose up.
Open a web browser to http://localhost:8000/phppgadmin/
Create a table, then navigate to the Browse tab of the new table.
Click the submit button. Observe the 404.

docker-compose.yml.txt
nginx.conf.txt