Context

I have a dockerized QGIS server project running and serving tiles through an OGC WMTS.

E.g. this URL:

http://{baseurl}/?SERVICE=WMTS&VERSION=1.3.0&REQUEST=GetTile&LAYER={my_custom_layer}&STYLE=default&TileMatrixSet=EPSG:3857&TileMatrix=22&TileRow=1079050&TileCol=2274423&format=image/png

shows me a tile in Firefox:

This works great.

But this is an HTTP request and I need to enable HTTPS.

If I query the same tile using HTTPS instead of HTTP, I have to wait forever, nothing happens, and the server stdout doesn't display any incoming requests.

Question

How could I enable HTTPS in my QGIS server?
I didn't find any information about it, either here or there.

Environment

The aforementioned docker image hosted on a Ubuntu 18.04 server machine.
Which gives:

# qgis --version
QGIS 3.10.6-A Coruña 'A Coruña' (ec80021f49)