Connect to SSL server using connect_ssl

I am using haproxy as a authorization layer, using a lua script. Since the lua code is being run in haproxy, I can’t use the luasocket and luasec libraries. So I am trying to use the connect_ssl function from haproxy to connect to my internal SSL server:

addr = “x.x.x.x”
port = 443
req = “GET “https://myserver/…” -H “accept: /””
local socket = core.tcp()
if socket:connect_ssl(addr, port) then
if socket:send(req) then

I could not find any documentation on how to pass the user certificate and key using the connect_ssl function. Has anyone used the connect_ssl with a certificate and key?
Thanks for the help.