Update SSL config.

While proofreading the config, and checking if it was up to date
according to:

- Mozilla recommandations
- SSLtest
- testssl.sh

I spotted an issue in the HSTS header:

$ curl -I https://afpy.org
[...]
Strict-Transport-Security: max-age=63072000; always

the `always` part is an nginx config token, not a cookie value.

So I simplified the conf so we can more easily copy/paste from Mozilla
generator, which obviously removed the bug.

roles/nginx/README.md

@@ -17,12 +17,7 @@ Optional variables are:
 
 - `nginx_owner`: If a unix user has to be created for this project.
 - `nginx_path`: To create a directory owned by `nginx_owner`.
-- `ssl_ciphers`: [Specifies the enabled ciphers](http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_ciphers).
-- `ssl_protocols`: [Enables the specified protocols.](http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_protocols)
-- `ssl_prefer_server_ciphers`: [Specifies that server ciphers should be preferred over client ciphers when using the SSLv3 and TLS protocols.](http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_prefer_server_ciphers)
-- `ssl_session_cache`: [Sets the types and sizes of caches that store session parameters.](http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_session_cache).
-- `HSTS_header`: HTTP header to inject.
-
+- `certbot_authenticator`: Defaults to `gandi`, can use `nginx`.
 
 ### Author Information
 

roles/nginx/defaults/main.yml

@@ -1,10 +1,7 @@
 ---
-ssl_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_protocols: "TLSv1.2 TLSv1.3"
+
 certbot_authenticator: gandi
-ssl_prefer_server_ciphers: "off"
-ssl_session_cache: "shared:ssl_session_cache:10m"
-HSTS_header: 'Strict-Transport-Security "max-age=63072000; always"'
+
 nginx_conf: |
   server
   {

roles/nginx/templates/letsencrypt.conf.j2

@@ -1,21 +1,27 @@
-# Inspired from
-# https://ssl-config.mozilla.org/#server=nginx&version=1.14.2&config=intermediate&openssl=1.1.1d&guideline=5.6
-ssl_ciphers "{{ ssl_ciphers }}";
-ssl_protocols {{ ssl_protocols }};
-ssl_prefer_server_ciphers {{ ssl_prefer_server_ciphers }};
+# generated 2023-01-13, Mozilla Guideline v5.6, nginx 1.17.7, OpenSSL 1.1.1k, intermediate configuration
+# https://ssl-config.mozilla.org/#server=nginx&version=1.17.7&config=intermediate&openssl=1.1.1k&guideline=5.6
 
-ssl_session_cache {{ ssl_session_cache }};
 ssl_session_timeout 1d;
+ssl_session_cache shared:MozSSL:10m;  # about 40000 sessions
 ssl_session_tickets off;
 
 ssl_certificate /etc/letsencrypt/live/{{ nginx_domain }}/fullchain.pem;
 ssl_certificate_key /etc/letsencrypt/live/{{ nginx_domain }}/privkey.pem;
+
+# curl https://ssl-config.mozilla.org/ffdhe2048.txt > /path/to/dhparam
 ssl_dhparam /etc/ssl/certs/dhparam.pem;
 
+# intermediate configuration
+ssl_protocols TLSv1.2 TLSv1.3;
+ssl_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_prefer_server_ciphers off;
+
+# HSTS (ngx_http_headers_module is required) (63072000 seconds)
+add_header Strict-Transport-Security "max-age=63072000" always;
+
+# OCSP stapling
 ssl_stapling on;
 ssl_stapling_verify on;
-ssl_trusted_certificate /etc/ssl/certs/ca-certificates.crt;
 
-{% if HSTS_header %}
-add_header {{ HSTS_header }};
-{% endif %}
+# verify chain of trust of OCSP response using Root CA and Intermediate certs
+ssl_trusted_certificate /etc/ssl/certs/ca-certificates.crt;