Google Home integration over Cloudflare


I want to use Home Assistant as an interface into Google Home in order to avoid the messy dual account Google Home setup when two Hue bridges are involved.
Remote access is performed over Cloudflare with url. ( not the real name … )
The google assistant integration specifies the requirement for a remote access url in
the form of
Testing this in a web browser fails as well as the initial authentication from an android Google home instance with the Google Assistant integration on the HA server, the error message being

Logging in with home assistant local
Error: invalid client id.

Setting up without the 8123 port number fails in the same way.
Searching for this issue in Google did not provide any answer.

So the question here : is this possible with Cloudflare, and if so how ?
or is there another free remote access solution that allows Google Assistant integration.
( I know Home Assistant Cloud does exactly this, but at a monthly cost )

Same here.
Have you found a solution?

same issue here…
Could you solve it?

ok… I made it. I leave you a post with everything I did in case you want to try it