Issue with HAProxy and Exchange 2016 with certificate based authentication

[CptTweek]

Hello!

I have an Exchange 2016 as a backend that requires client certificates for accessiong OWA and HAProxy as a reverse proxy. When I try to open OWA from Exchange directly everything is fine: I get a certificate prompt and can choose one that I want. But when I do the same through HAProxy I only get certificate prompt for HAProxy and then browser redirects me to Exchange authentication page without prompting certificate. The part of my config is below.

frontend fe_exch_443
    bind    x.x.x.x:443 ssl crt /etc/ssl/certs/cert.pem ca-file /etc/ssl/certs/cert.crt verify optional crt-ignore-err all
acl ssl_connection ssl_fc
    acl path_owa path_beg -i /owa/
    http-request deny if path_check
    http-request redirect scheme https code 301 if !{ ssl_fc }
    use_backend bk_exchange_https_owa if path_owa
    default_backend be_exch_443
backend bk_exchange_https_owa
    option httpchk GET /owa/HealthCheck.htm
    http-check expect string 200\ OK
    server  exch        x.x.x.x:443  check ssl verify none maxconn 1000 weight 10 check

Any ideas? Thank you!