Use nginx's official repo and improve TLS configuration

These packagea are newer than the 15.04 we had. We can enable HTTP2

site-cookbooks/kosmos-nginx/files/default/nginx_tls_config.conf

@@ -0,0 +1,14 @@
+# Improve performance
+ssl_session_timeout 1d;
+ssl_session_cache shared:SSL:50m;
+ssl_session_tickets off;
+# Disable insecure cyphers
+ssl_protocols TLSv1.2;
+ssl_prefer_server_ciphers on;
+# From https://mozilla.github.io/server-side-tls/ssl-config-generator/
+# Oldest compatible clients: Firefox 27, Chrome 30, IE 11 on Windows 7, Edge, Opera 17, Safari 9, Android 5.0, and Java 8
+# We don't have a lot of those cyphers (using Ubuntu 15.04), but CBC is insecure:
+# https://blog.cloudflare.com/yet-another-padding-oracle-in-openssl-cbc-ciphersuites/
+ssl_ciphers 'ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256';
+# Unique DH Group, see https://weakdh.org/sysadmin.html
+ssl_dhparam /etc/ssl/private/dhparams.pem;

site-cookbooks/kosmos-nginx/metadata.rb

@@ -8,3 +8,4 @@ version          '0.1.0'
 
 depends 'nginx'
 depends 'firewall'
+depends 'openssl'

site-cookbooks/kosmos-nginx/recipes/default.rb

@@ -22,9 +22,26 @@ node.override['nginx']['log_formats']['json']  = <<-EOF
 '"ua":"$http_user_agent"}'
 EOF
 
-
+node.override['nginx']['repo_source'] = 'nginx' # Install from official repo
+node.override['nginx']['upstream_repository'] = "http://nginx.org/packages/mainline/#{node['platform']}"
 include_recipe 'nginx'
 
+# Generate Strong Diffie-Hellman Group (increases security)
+# https://weakdh.org/sysadmin.html
+openssl_dhparam "/etc/ssl/private/dhparams.pem" do
+  key_length 2048
+  mode 0600
+  owner 'www-data'
+end
+
+cookbook_file "#{node['nginx']['dir']}/conf.d/tls_config.conf" do
+  source 'nginx_tls_config.conf'
+  owner  'root'
+  group  'root'
+  mode   '0644'
+  notifies :restart, 'service[nginx]'
+end
+
 unless node.chef_environment == "development"
   include_recipe 'kosmos-base::firewall'