Tighten default TLS settings to attain A+ rating by default

[bvansomeren]

The current defaults leave some ciphers enabled that shouldn't be used (CBC mode for AES for example); Also HSTS isn't set. Change the settings to allow modern browsers.

Example from Mozilla:

haproxy 2.1, intermediate config, OpenSSL 1.1.1d Supports Firefox 27, Android 4.4.2, Chrome 31, Edge, IE 11 on Windows 7, Java 8u31, OpenSSL 1.0.1, Opera 20, and Safari 9 https://ssl-config.mozilla.org/#server=haproxy&version=2.1&config=intermediate&openssl=1.1.1d&guideline=5.6

generated 2021-05-07, Mozilla Guideline v5.6, HAProxy 2.1, OpenSSL 1.1.1d, intermediate configuration

https://ssl-config.mozilla.org/#server=haproxy&version=2.1&config=intermediate&openssl=1.1.1d&guideline=5.6

global

intermediate configuration

ssl-default-bind-ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
ssl-default-bind-ciphersuites TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
ssl-default-bind-options prefer-client-ciphers no-sslv3 no-tlsv10 no-tlsv11 no-tls-tickets

ssl-default-server-ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
ssl-default-server-ciphersuites TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
ssl-default-server-options no-sslv3 no-tlsv10 no-tlsv11 no-tls-tickets

# curl https://ssl-config.mozilla.org/ffdhe2048.txt > /path/to/dhparam
ssl-dh-param-file /path/to/dhparam

frontend ft_test mode http bind :443 ssl crt /path/to/<cert+privkey+intermediate> alpn h2,http/1.1 bind :80 redirect scheme https code 301 if !{ ssl_fc }

# HSTS (63072000 seconds)
http-response set-header Strict-Transport-Security max-age=63072000