haproxy ssl support

[Rok Potočnik]

Even though it seems dovecot (using 2.2.33.1) supports haproxy's 
send-proxy-v2, it seems to lack send-proxy-v2-ssl (which also sends 
client's ssl state). It would be a nice feature for the backend server 
to identify clients so one wouldn't have to use disable_plaintext_auth 
on a production environment.

--- haproxy.cfg
frontend pop3
         bind [::]:110 v4v6
         bind [::]:995 v4v6 ssl crt /etc/pki/tls/private/haproxy.pem
         mode tcp
         default_backend pop3
backend pop3
     mode tcp
     balance leastconn
     stick store-request src
     stick-table type ip size 200k expire 30m
     timeout connect 5000
     timeout server  50000
     server proxy1 [2001:db8::11]:10110 send-proxy-v2-ssl
     server proxy2 [2001:db8::22]:10110 send-proxy-v2-ssl
---

--- dovecot.conf
haproxy_trusted_networks = [2001:db8::]/64
service pop3-login {
   inet_listener pop3_haproxy {
     port = 10110
     haproxy = yes
   }
}
---

It would also be nice if haproxy would support STARTTLS offloading but 
that's a subject for a different mailing list ;)

-- 
BR, Rok