Reverse Proxy Requirements

General
Nginx Proxy Example

General

The Simplifier Server needs a typcial Reverse Proxy as standard setup.

The Reverse Proxy should provide the following services for a secure setup

SSL Offloading
Virus / Malware Scanning
Web Application Firewall

Forwarded Ports:

443 (HTTPS)

Port 443

HTTPS (valid certificate)
modern, secure TLS configuration (incl. HTTP Strict Transport Security)
HTTP2 if possible
Header:
- “Upgrade”: Pass from client (for WebSockets)
- “X-Real-IP”: IP address of the client
- “X-Forwarded-Forwarded-For”: Remote address of the client, or X-Forwarded-For Header of the parent proxy server.
- “X-Forwarded-Proto”: Original protocol of the request (“http” or “https”)
- CORS Headers (see below)
- (Temporary) Redirect from “/” to either AdminUI (“/UserInterface/”) or App of choice (“/appDirect/$appName”)
- Proxy connection/read/send Timeout to high value, e. g. 10 min
- Maximum body size (post, put) to appropriate value, e. g. 20 MB (doesn’t have to be too big, because packets > 20 MB are transferred as single chunks)
- Proxy forwarding to Simplifier AppServer port 8080 (if on another server, must be reachable via firewall)

Proxy must be able to pass through WebSocket connections!

CORS headers

Cross-Origin Resource Sharing (CORS) is a mechanism that uses additional HTTP headers to allow a user agent to access selected resources from a server located on a different origin (domain) than the currently used Web site. A user agent makes a cross-origin HTTP request when requesting a resource from another domain, protocol, or port than the one from which the current document originates.

The CORS mechanism supports secure cross-domain queries and data transfers between browsers and web servers. Modern browsers use CORS in an API container such as XMLHttpRequest or Fetch to minimize the risks of cross-origin HTTP requests.

For request methods’ POST’,’ GET’,’ PUT’,’ DELETE’,’PATCH’:

Header name	Header value
Access-Control-Allow-Origin	*
Access-Control-Allow-Credentials	true
Access-Control-Allow-Methods	GET, POST, PUT, DELETE, OPTIONS, PATCH
Access-Control-Allow-Headers	DNT, X-CustomHeader, Keep-Alive, User-Agent, X-Requested-With, If-Modified-Since, Cache-Control, Content-Type, Authorization, SimplifierToken, SimplifierApp, SimplifierModule, SimplifierModuleInterface, SimplifierClientBusinessObject, SimplifierClientBusinessObjectFunction, sap-cancel-on-close, sap-contextid-accept, MaxDataServiceVersion, DataServiceVersion, Content-Length, SimplifierApiKey, OData-MaxVersion, OData-Version, MIME-Version, X-CSRF-Token
Access-Control-Expose-Headers	remainingTokenLifetime,OData-Version

Additionally for request method ‘OPTIONS’:

Header name	Header value
Access-Control-Max-Age	1728000
Response name	Response code
Empty Content	204, No proxy call required

The following paths should be configured for routing it back to Simplifier

Location / Path	Description
“^/genToken/$”	The Simplifier Authentification Service based on Tokens
“^/assets/(.*)$”	The static assets like images, pdf files, etc for an Application
“^/client/(.*)$”	The Client REST API to access business objects, connector or plugins
“^/library-managed/(.*)$”	Third-Party Javascript Libraries that need for the HTML5 Applications
“^/library-static/(.*)$”	Third-Party Javascript Libraries that need for the HTML5 Applications
“^/appDirect/(.*)$”	Hosting Path for the created HTML5 Applications
“^/UserInterface/(.*)$”	Admin Backend Interface Application (should only accessible in a secure environment, internal network)
“^/authentication/(.*)$”	External Authentication Provider for e.g. oAuth
“^/passwordExpired/(.*)$”	Password Reset Page for Admin Interface
“^/develop/(.*)$”	Plugin Interface
“^/system-library/(.*)$”	System Libraries like OpenUI5
“^/appwizard/(.*)$”	REST API for App Wizards

Nginx Proxy Example

To fulfill all mandatory requirements, you can use the following example of a nginx reverse proxy configuration:

# Run as a less privileged user for security reasons.
user nginx;

worker_processes auto;

events {
  worker_connections 1024;
}

pid        /var/run/nginx.pid;



http {
	# If we receive X-Forwarded-Proto, pass it through; otherwise, pass along the
	# scheme used to connect to this server
	map $http_x_forwarded_proto $proxy_x_forwarded_proto {
	  default $http_x_forwarded_proto;
	  ''      $scheme;
	}
	# If we receive Upgrade, set Connection to "upgrade"; otherwise, delete any
	# Connection header that may have been passed to this server
	map $http_upgrade $proxy_connection {
	  default upgrade;
	  '' close;
	}

    #Redirect to https, using 307 instead of 301 to preserve post data
    server {
    server_name localhost;
    listen 80;
    return 307 https://$host$request_uri;
    }

    server {
        listen [::]:443 ssl;
        listen 443 ssl http2;

        server_name localhost;

        # Protect against the BEAST attack by not using SSLv3 at all. If you need to support older browsers (IE6) you may need to add
        # SSLv3 to the list of protocols below.
        ssl_protocols              TLSv1.2;

        # Ciphers set to best allow protection from Beast, while providing forwarding secrecy, as defined by Mozilla - https://wiki.mozilla.org/Security/Server_Side_TLS#Nginx
        ssl_ciphers                ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:ECDHE-RSA-RC4-SHA:ECDHE-ECDSA-RC4-SHA:AES128:AES256:RC4-SHA:HIGH:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK;
        ssl_prefer_server_ciphers  on;

        # Optimize TLS/SSL by caching session parameters for 10 minutes. This cuts down on the number of expensive TLS/SSL handshakes.
        # The handshake is the most CPU-intensive operation, and by default it is re-negotiated on every new/parallel connection.
        # By enabling a cache (of type "shared between all Nginx workers"), we tell the client to re-use the already negotiated state.
        # Further optimization can be achieved by raising keepalive_timeout, but that shouldn't be done unless you serve primarily HTTPS.
        ssl_session_cache    shared:SSL:10m; # a 1mb cache can hold about 4000 sessions, so we can hold 40000 sessions
        ssl_session_timeout  24h;


        # Use a higher keepalive timeout to reduce the need for repeated handshakes
        keepalive_timeout 300; # up from 75 secs default

        # remember the certificate for a year and automatically connect to HTTPS
        add_header Strict-Transport-Security 'max-age=31536000; includeSubDomains';

        ssl_certificate      /etc/nginx/ssl.crt;
        ssl_certificate_key  /etc/nginx/ssl.key;


        location / {
            proxy_pass http://simplifier:8080; # TODO: replace port if app listens on port other than 80
            
            proxy_connect_timeout       600;
            proxy_send_timeout          600;
            proxy_read_timeout          600;
            send_timeout                600;
            client_max_body_size        20m;

			proxy_http_version 1.1;
			proxy_buffering off;
            proxy_set_header Host $http_host;
            proxy_set_header X-Real-IP $remote_addr;
			proxy_set_header Upgrade $http_upgrade;
			proxy_set_header Connection $proxy_connection;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
			proxy_set_header X-Forwarded-Proto $proxy_x_forwarded_proto;

       if ($request_method = 'OPTIONS') {
            add_header 'Access-Control-Allow-Origin' '*';
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS, PATCH';
            add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,SimplifierToken,SimplifierApp,remainingTokenLifetime';
            add_header 'Access-Control-Expose-Headers' 'remainingTokenLifetime,OData-Version';
            add_header 'Access-Control-Max-Age' 1728000;
            add_header 'Content-Type' 'text/plain charset=UTF-8';
            add_header 'Content-Length' 0;
            return 204;
        }
        if ($request_method = 'POST') {
            add_header 'Access-Control-Allow-Origin' '*';
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS, PATCH';
            add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,SimplifierToken,SimplifierApp,remainingTokenLifetime';
            add_header 'Access-Control-Expose-Headers' 'remainingTokenLifetime,OData-Version';
        }
        if ($request_method = 'GET') {
            add_header 'Access-Control-Allow-Origin' '*';
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS, PATCH';
            add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,SimplifierToken,SimplifierApp,remainingTokenLifetime';
            add_header 'Access-Control-Expose-Headers' 'remainingTokenLifetime,OData-Version';
        }
        if ($request_method = 'PUT') {
            add_header 'Access-Control-Allow-Origin' '*';
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS, PATCH';
            add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,SimplifierToken,SimplifierApp,remainingTokenLifetime';
            add_header 'Access-Control-Expose-Headers' 'remainingTokenLifetime,OData-Version';
        }
        if ($request_method = 'DELETE') {
            add_header 'Access-Control-Allow-Origin' '*';
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS, PATCH';
            add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,SimplifierToken,SimplifierApp,remainingTokenLifetime';
            add_header 'Access-Control-Expose-Headers' 'remainingTokenLifetime,OData-Version';
        }
        if ($request_method = 'PATCH') { 
            add_header 'Access-Control-Allow-Origin' '*'; 
            add_header 'Access-Control-Allow-Credentials' 'true';
            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS, PATCH';
            add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Authorization,SimplifierToken,SimplifierApp,remainingTokenLifetime';
            add_header 'Access-Control-Expose-Headers' 'remainingTokenLifetime,OData-Version'; 
        }
            location = / {
            return 302 https://$host/UserInterface/;
            }
        }
    }
}

In this Example the

proxy_pass http://simplifier:8080;

refers to a docker container name and only works if the nginx container running in the same container group.

Requirements