HTTP CONNECT request returns 4XX

[Bowen Ni]

Hi,

I am trying to use HAProxy as a man-in-the-middle proxy for HTTPS 
traffic. When doing an HTTPS request over HAProxy, it tries to tunnel 
the HTTPS request using an HTTP CONNECT request and the HTTP CONNECT 
request is passed to backend server directly. My problem is that the 
response of the CONNECT request I got from HAProxy is always 4XX. For 
example: 403 Tunnel Forbidden, 400 Bad Request. I have tried many 
backends and none of them give me 200. Am I missing anything?


I looked into some other proxies 
(https://mitmproxy.org/doc/explicit_https.png and 
http://www.charlesproxy.com/documentation/proxying/ssl-proxying/). It 
seems that they are replying 200 OK at the proxy immediately without 
forwarding it to the backends. Is it possible to do the same in HAProxy?

Best, Bowen