web: split TLS configuration and make it stronger

Resources:

- https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
- https://weakdh.org/sysadmin.html

web/rootfs/defaults/ssl.conf

@@ -0,0 +1,16 @@
+# session settings
+ssl_session_timeout 1d;
+ssl_session_cache shared:SSL:50m;
+ssl_session_tickets off;
+
+# Diffie-Hellman parameter for DHE cipher suites
+ssl_dhparam /config/nginx/dhparams.pem;
+
+# ssl certs
+ssl_certificate /config/keys/cert.crt;
+ssl_certificate_key /config/keys/cert.key;
+
+# protocols
+ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
+ssl_prefer_server_ciphers on;
+ssl_ciphers ECDH+AESGCM:ECDH+CHACHA20:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:RSA+AESGCM:RSA+AES:!aNULL:!MD5:!DSS;