There is mismatch between HTTPS indicated on the server and client - php

Question

This is the warning when I open my phpMyAdmin's login (index) page:
There is mismatch between HTTPS indicated on the server and client.
This can lead to non working phpMyAdmin or a security risk.
Please fix your server configuration to indicate HTTPS properly.
The error should be caused by a loadbalancer in between my client and phpmyadmin itself. SSL terminates on the loadbalancer so the URL being used (that phpmyadmin receives in request headers, I assume) is https://mydomain/phpmyadmin.
The loadbalancer communicates with phpmyadmin via http, so the URL being used between lb and pma is http://mydomain/phpmyadmin (not https).
I found this very fitting article on github: Possibility to deactivate SSL connection #170 which is for Docker containers and describes an env var to be passed to the container called "PMA_ABSOLUTE_URI" to fix the problem.
Which setting would this be in phpmyadmin NON Docker?
Any other solution to my problem is also highly appreciated.
Sidenote: Phpmyadmin works fine after the login. You can log in, there are no warnings after the log in and you can perform all interactions without problems. I am just worried about the warning.

Answer 1

I have exactly the same setup as you are describing. A front load balancer acts as reverse proxy and also as SSL/TLS terminator. The LB talks in plain http with the backend server where phpMyAdmin is running.
When I upgraded from 4.0.4.1 to 4.9.0.1 I got the same warning appearing at the phpMyAdmin login screen as you. I was able to solve this on the reverse proxy by "faking" the protocol from http to https. In my case my reverse proxy is a Nginx web server and just before I'd pass to the backend server, I added X-Forwarded-Proto:
server {
listen 443;
server_name my.phpmyadmin.example.com;
[... log and ssl settings ...]
location / {
include /etc/nginx/proxy.conf;
proxy_set_header X-Forwarded-Proto https;
proxy_pass http://backendserver;
}
}
By adding proxy_set_header X-Forwarded-Proto https; this tells the backend server that the client to proxy communication happens over https. Without setting this header, phpMyAdmin probably identifies (not sure, just a guess) that it was loaded on a https:// URL yet the communication (between reverse proxy and phpMyAdmin server) happened over http. Therefore it's a correct warning to be shown.
As soon as Nginx was reloaded, the warning disappared from the phpMyAdmin login screen.