Hello,
I wish I can export my new/next game on all platforms (HTML5 , android , windows .. ).
I use TCP_server to listen for a specific incoming connection (redirect after a succefull login )
It works well on windows but not with an HTML5 export ... do you have any clue ?

I would imagine it's a security issue. HTML5 has greatly sandboxed features compared to desktop and you don't have full access. You might either have to adjust security on your server, or use Javascript. But I don't know specifically about that error.

I was thinking of changing the way I'm doing it.
One way is to have different function one for each kind : HTML5 / Android / heavy client
Or an auth proxy server somewhere else which does the same thing as my TCP Server and regular request on this

It brings some security issues ( one more server, man in the middle ) but it is the easiest way

I don't think TCPServer works with HTML5 builds, they're ultimately just browser javascript and are limited by what the browser can do. According to the docs:

the HTML5 platform currently offers WebSockets and WebRTC support but lacks some of the higher-level features, as well as raw access to low-level protocols like TCP and UDP.