Issue with websocket behind nginx behind a haproxy SNI TLS reverse proxy

[noci]

the haproxy is conforming to the following setup:

http://blog.haproxy.com/2012/04/13/enhanced-ssl-load-balancing-with-server-name-indication-sni-tls-extension/

Look for:
Choose a server using SNI: aka SSL routing

No certificates available to haproxy, so no decoding and/or adding removing
headers. 
disecting of traffic is purely based on SSL Client Hello providing an SNI.
(tcp mode forwarding)

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,271128,271164#msg-271164