Secure Your Application on SAP Cloud Platform Cloud Foundry

Before we dive deeper into the real setup of the architecture, let’s quickly review the architecture we intend to go for.

Figure 1 presents the final setup. First, we still have our existing “Hello World” or “Business Partner” Java-based microservice that we have created in the previous tutorials. However, instead of letting the customer access this application directly, we will use the so-called Application Router (App Router) that serves two purposes.

On the one hand, the App Router is a general entry point into the world of microservices. The main idea is that you can split an application into multiple microservices with independent deployability, polyglot runtimes & persistence and independent teams. Therefore, a central entry component is required that hides the complexity of the microservice landscape from the end customer.

On the other hand, the App Router is mainly responsible for managing authentication flows. The App Router takes incoming, unauthenticated requests from users and initiates an OAuth2 flow with the Extended Services for User Account and Authentication (XSUAA). The XSUAA service is an SAP-specific extension of CloudFoundry's UAA service to deal with authentication and authorization (it may again delegate this aspect to other providers such as external Identity Providers, see later in this tutorial). If the user authenticates at the XSUAA, it will respond with a JSON Web Token (JWT) containing the authenticated users as well as all scopes that he or she has been granted.

Figure 1: Authentication Flow during Runtime

The JWT s passed by the App Router to the underlying microservices so that they are freed up from this task. At the same time, these microservices can only be accessed with a valid JWT, hence, are protected from unauthenticated traffic.

The JWT contains a signature that needs to be verifiable by every microservice to establish trust. Hence, every service require a key (client-secrets or public keys) to verify this signature and reject any requests with non-valid JWTs. Therefore, every service has to maintain a service binding to the XSUAA that provides this information for runtime verification (Figure 2). To enable this, every microservice binds to a dedicated XSUAA instance which writes this information into the VCAP_SERVICES environment variable which the microservices can use to verify any token’s validity.

Figure 2: Provisioning view with XSUAA binding

With these basics in mind, let’s create the picture of Figure 1 and Figure 2 by setting up the App Router, XSUAA and backend microservices to enable full application security.

The App Router can be installed in two different ways: (1) Download from Service Marketplace and (2) Download from the SAP NPM Registry. These steps are explained below:

Alternative 1: Get the App Router via Service Marketplace

1. Before you can start the setup and configuration of the App Router component you need to download the XSA Javascript package from Service Marketplace: https://launchpad.support.sap.com/#/softwarecenter/template/products/%20_APP=00200682500000001943&_EVENT=DISPHIER&HEADER=Y&FUNCTIONBAR=N&EVENT=TREE&NE=NAVIGATE&ENR=73554900100200003885&V=MAINT&TA=ACTUAL&PAGE=SEARCH/XS%20JAVASCRIPT%201. At the time of writing the package XS_JSCRIPT14_3-70001363.ZIP is the most recent one.

2. After downloading the package extract it to your favorite <location>

3. cd <location>/@sap

4. Copy the approuter directory to some newly created directory that we call <destLocation>

This alternative approach requires that you have npm installed on your machine.

1. Go to your favourite and create the approuter directory

   cd <destLocation>
   mkdir approuter
   cd approuter
   

2. Place the following package.json in your approuter directory

   {
     "name": "approuter",
     "dependencies": {
       "@sap/approuter": "*"
     },
     "scripts": {
       "start": "node node_modules/@sap/approuter/approuter.js"
     }
   }
   

3. Install AppRouter dependencies using the following commands

   npm config set @sap:registry https://npm.sap.com
   npm install
   

1. Within /approuter create a new file called xs-app.json with the following content:

   {
     "welcomeFile": "index.html",
     "routes": [{
   "source": "/",
   "target": "/",
   "destination": "app-destination"
     }]
   }
   

2. Within create a new manifest.yml file for the AppRouter microservice with the following content.

---
applications:
- name: approuter
  host: approuter-p1942765239trial
  path: approuter
  memory: 128M
  buildpack: nodejs_buildpack
  env:
    TENANT_HOST_PATTERN: 'approuter-(.*).cfapps.eu10.hana.ondemand.com'
    destinations: '[{"name":"app-destination", "url" :"https://firstapp-p1942765239trial.cfapps.eu10.hana.ondemand.com", "forwardAuthToken": true}]'
  services:
    - my-xsuaa

Adapt the TENANT_HOST_PATTERN in the manifest.yml file to the host of the Cloud Foundry region you are running on; the above assumes EU (eu10).

Understanding the AppRouter’s manifest.yml and xs-app.json:

The TENANT_HOST_PATTERN is a variable that declares the pattern how multiple tenants in the URL are identified and handled. During runtime, the App Router will match the incoming host against the pattern and tries to extract the regular expression from the pattern. It will use the matched string to delegate authentication to the respective XSUAA tenant (in SAP Cloud Platform the tenant ID corresponds to the subaccount ID. If you desire different URL patterns, you need to change this pattern accordingly.

Note that the TENANT_HOST_PATTERN variable is only required in real multi-tenant application, i.e, applications where a physical deployment serves multiple clients from the same deployment. We assume in this blog series that we want to build multi-tenant applications, as we aim towards cloud-native development. However, this variable is not necessary if you have a single-tenant application. To realize this, the xs-security.json security descriptor may declare tenant-mode: dedicated (see step 5 below).

Destinations is a variable that declares the internal routes from the App Router to the underlying backend microservices. As we only have one hello world microservice yet, we define only one destination called app-destination here. This app-destination is referenced by the previously created xs-app.json file.

The services section declares to bind our own XSUAA service instance to the App Router. This binding will ensure a corresponding VCAP_SERVICE entry that holds the client ID, client secret and public key that is required to validate any incoming OAuth token/JWT from the XSUAA service:

1. Within the manifest.yml replace the destinations variable with the specific URL to your Java backend service used in the previous tutorials. In my case, the URL is

https://firstapp-p1942765239trial.cfapps.eu10.hana.ondemand.com

1. Within the manifest.yml replace the host name to your unique host identifier by using approuter-. In my case the host name is

   approuter-p1942765239trial
   

2. Now we need to create a service binding to the XSUAA service. As a prerequisite we require an xs-security.json (security descriptor) file that contains a declaration about authorization scopes we intend to use in our application. In our case, we simply declare a DISPLAY scope that we will use later on to authorize our users. In addition, we declare a so-called role template called Viewer that references our DISPLAY scope.

   We put this file to <destLocation>/xs-security.json. For a more detailed explanation on scopes and role templates, see the appendix of this tutorial. More details on the syntax of the xs-security.json can be found here.

   Note that the xsappname has to be unique within the entire XSUAA instance. We follow here the same pattern using our -. In my case this is firstapp-p1942765239trial.

   Note that as explained above, tenant-mode: shared assumes a multi-tenant application and will require the TENANT_HOST_PATTERN variable to be declared. You may also use “tenant-mode”: “dedicated” if you develop a single-tenant application.

   {
     "xsappname": "firstapp-p1942765239trial",
     "tenant-mode": "shared",
     "scopes": [
       {
         "name": "$XSAPPNAME.Display",
         "description": "display"
       }
     ],
     "role-templates": [
       {
         "name": "Viewer",
         "description": "Required to view things in our solution",
         "scope-references"     : [
           "$XSAPPNAME.Display"
         ]
       }
     ]
   }
   

6. We then create a service instance called my-xsuaa of the XSUAA service by issuing the following command and using the xs-security.json file:

cf create-service xsuaa application my-xsuaa -c xs-security.json

• If you have created this instance of the XSUAA service before without the xs-security.json parameter, you can unbind and delete the existing instance with these commands before creating it with the above command:

  cf unbind-service firstapp my-xsuaa
  cf delete-service my-xsuaa​
  

7. Before we deploy your folder structure should look similar to this:

You may have different content in the approuter folder depending on the download alternative you have chosen. Ensure that xs-app.json and package.json and the node_modules directory with content are present.

8. Then deploy the AppRouter using the following (with the appropriate API endpoint of your Cloud Foundry region):

cd <destLocation>
cf api https://api.cf.eu10.hana.ondemand.com
cf login
cf push

9. Afterwards you should be able to locate the App Router from within your browser using the host name of your deployment. In my case this is https://approuter-p1942765239trial.cfapps.eu10.hana.ondemand.com/hello which should face you with the following login page where you can use your user e-mail and password:

10. After logging in you should see the HelloWorld servlet which is now served by the App Router as a proxy to your Java application:

After authentication works with the App Router, your java backend service is still fully visible in the web and not protected. We, therefore, need to protect our java microservices as well so that they accept requests with valid JWTs for the current user only. In addition, we will setup the microservice in a way that it deals with authorization, i.e., understands the OAuth scopes from the JWT that we have configured previously using the xs-security.json file.

In the following, we will use the Spring Security framework to protect the microservices. You can also use standard mechanisms of the SAP Java buildpack to achieve the same. If you do not want to use Spring Security please follow the steps here, nonetheless, the concepts described hereinafter apply for both methods.

The first step is to get some additional Java libs from Service Marketplace. To get them, do the following steps:

1. Download additional XS security libs from service marketplace: https://launchpad.support.sap.com/#/softwarecenter/search/XS_JAVA
2. At the time of writing the latest package is XS_JAVA_1-70001362.ZIP (19.03.2018).
3. Unzip
4. Install XS Security Libs to your local maven repo using:

cd <destLocation>
mvn clean install

In the second step, we go back to our HelloWorld or Business Partner application and open the main application/pom.xml which looks similar to this structure:

In the <dependencies> section of the application/pom.xml, we enhance the following additional dependencies to our project:

<!-- Authentication and Authorization imports with Spring Security -->
<dependency>
  <groupId>com.sap.xs2.security</groupId>
  <artifactId>security-commons</artifactId>
  <version>0.28.6</version>
</dependency>
<dependency>
  <groupId>com.sap.xs2.security</groupId>
  <artifactId>java-container-security</artifactId>
  <version>0.28.6</version>
</dependency>
<dependency>
  <groupId>com.sap.xs2.security</groupId>
  <artifactId>java-container-security-api</artifactId>
  <version>0.28.6</version>
</dependency>
<dependency>
  <groupId>org.springframework.security</groupId>
  <artifactId>spring-security-jwt</artifactId>
  <version>1.0.9.RELEASE</version>
</dependency>
<dependency>
  <groupId>org.springframework.security.oauth</groupId>
  <artifactId>spring-security-oauth2</artifactId>
  <version>2.3.3.RELEASE</version>
</dependency>
<dependency>
  <groupId>com.sap.security.nw.sso.linuxx86_64.opt</groupId>
  <artifactId>sapjwt.linuxx86_64</artifactId>
  <version>1.1.19</version>
</dependency>

This dependency section contains three main parts of dependencies:

1. The org.springframework.security packages add certain aspects of the Spring security framework to our application, in particular the OAuth framework of Spring security.
2. The com.sap.xs2.security packages contain specific security adaptations for the CloudFoundry/XSA environment.
3. The com.sap.security.nw.sso.linuxx86_64.opt packages contain platform-specific native implementations for the JWT validation.

Afterwards you need to go to your web.xml in src/main/webapp/WEB-INF and add the following lines. If you have used the Archetype in Step 3 of the Tutorial: https://blogs.sap.com/2017/05/19/step-3-with-sap-s4hana-cloud-sdk-helloworld-on-scp-cloudfoundry/ these lines should be already there and you can simply uncomment them.

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/spring-security.xml</param-value>
</context-param>
<filter>
    <filter-name>springSecurityFilterChain</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
    <filter-name>springSecurityFilterChain</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

This configuration introduces the Spring Security Filter Chain on all incoming routes of your Java microservice and declares that the entire security configuration can be found in a file called spring-security.xml.

In the next step we need to protect our routes on a more fine-grained basis by introducing the file spring-security.xml to our /src/main/webapp/WEB-INF directory. If you have used the Archetype in Step 3 of the Tutorial: https://blogs.sap.com/2017/05/19/step-3-with-sap-s4hana-cloud-sdk-helloworld-on-scp-cloudfoundry/ this file should be already there.

To protect all your routes so that users have to be at least authenticated you spring-security.xml should contain at least the following line:

<sec:intercept-url pattern="/**" access="isAuthenticated()" method="GET" />

This code says that all users which access all URLs under / with the GET method have to be at least authenticated. You can find the full reference for access management here: https://docs.spring.io/spring-security/site/docs/current/reference/html/el-access.html

The full spring-security.xml should look like this:

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:oauth="http://www.springframework.org/schema/security/oauth2"
   xmlns:sec="http://www.springframework.org/schema/security"

   xsi:schemaLocation="http://www.springframework.org/schema/security/oauth2
       http://www.springframework.org/schema/security/spring-security-oauth2-1.0.xsd
        http://www.springframework.org/schema/security
        http://www.springframework.org/schema/security/spring-security-3.2.xsd
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.1.xsd">

   <!-- protect secure resource endpoints ================================================ -->

   <sec:http pattern="/**" create-session="never"
      entry-point-ref="oauthAuthenticationEntryPoint"
      access-decision-manager-ref="accessDecisionManager"
      authentication-manager-ref="authenticationManager"
      use-expressions="true">
      <sec:anonymous enabled="false" />

      <!-- section to protect your endpoints -->

      <!-- Example: Check a specific OAuth Scope (i.e., authorization) on a resource -->
      <!--<sec:intercept-url pattern="/hello" access="#oauth2.hasScope('${xs.appname}.Display')" method="GET" />-->

      <!-- Example: Check only authentication on a resource -->
      <sec:intercept-url pattern="/**" access="isAuthenticated()" method="GET" />

      <sec:custom-filter ref="resourceServerFilter" before="PRE_AUTH_FILTER" />
      <sec:access-denied-handler ref="oauthAccessDeniedHandler" />
   </sec:http>

   <bean id="oauthAuthenticationEntryPoint"
      class="org.springframework.security.oauth2.provider.error.OAuth2AuthenticationEntryPoint">
   </bean>

   <bean id="oauthWebExpressionHandler"
      class="org.springframework.security.oauth2.provider.expression.OAuth2WebSecurityExpressionHandler">
   </bean>

   <bean id="accessDecisionManager"
      class="org.springframework.security.access.vote.UnanimousBased">
      <constructor-arg>
         <list>
            <bean class="org.springframework.security.web.access.expression.WebExpressionVoter">
               <property name="expressionHandler" ref="oauthWebExpressionHandler" />
            </bean>
            <bean class="org.springframework.security.access.vote.AuthenticatedVoter"  />
         </list>
      </constructor-arg>
   </bean>

    <sec:authentication-manager alias="authenticationManager"/>

   <oauth:resource-server id="resourceServerFilter"
      resource-id="springsec" token-services-ref="offlineTokenServices" />

   <bean id="offlineTokenServices"
         class="com.sap.xs2.security.commons.SAPOfflineTokenServices">
         <property name="verificationKey" value="${xs.uaa.verificationkey}" />
         <property name="trustedClientId" value="${xs.uaa.clientid}" />
         <property name="trustedIdentityZone" value="${xs.uaa.identityzone}" />
    </bean>

   <bean id="oauthAccessDeniedHandler"
      class="org.springframework.security.oauth2.provider.error.OAuth2AccessDeniedHandler" />

   <!-- define properties file =========================================================== -->
   <bean class="com.sap.xs2.security.commons.SAPPropertyPlaceholderConfigurer">
      <property name="location"  value="classpath:/application.properties" />
   </bean>
</beans>

Now we need to modify the manifest.yml a bit to interpret the JWT sufficiently. To do this add the following lines to your backend microservice’s manifest.yml file:

SAP_JWT_TRUST_ACL: '[{"clientid" : "*", "identityzone" : "*"}]'

In addition, we need to bind our my-xsuaa instance to our java backend service as well so that we have the OAuth secret to validate the JWT’s signature

services:
- my-xsuaa

In my example case, the final manifest.yml may look like this (depending on your progress with other steps of the tutorial):

---
applications:
- name: firstapp
  memory: 768M
  host: firstapp-p1942765239trial
  path: application/target/firstapp-application.war
  buildpack: sap_java_buildpack
  env:
    TARGET_RUNTIME: tomee
    JBP_CONFIG_SAPJVM_MEMORY_SIZES: 'metaspace:96m..'
    SAP_JWT_TRUST_ACL: '[{"clientid" : "*", "identityzone" : "*"}]'
  services:
  - my-destination
  - my-xsuaa

Now we are ready to build and deploy the application to try all our changes with

mvn clean install
cf push

After deployment, accessing your backend service should not be possible anymore and will quit with the following message:

However, you should be still able to access your application using the App Router as the entrypoint:

If you have previously enabled the mocking of tenant and user information via the environment variable ALLOW_MOCKED_AUTH_HEADER as mentioned in Step 5 of this tutorial series, you should now remove this setting. Execute the following command:

cf unset-env firstapp ALLOW_MOCKED_AUTH_HEADER

If you have previously exposed the backing service directly to the end user, you have used the RestCsrfPreventionFilter on the backend to protect against [Cross-Site-Request-Forgery]. As this is now in the responsibility of the App Router, we should remove it. For this remove the following lines from your web.xml:

<filter>
  <filter-name>RestCsrfPreventionFilter</filter-name>
  <filter-class>org.apache.catalina.filters.RestCsrfPreventionFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>RestCsrfPreventionFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

Now that we saved the backend microservice from unauthenticated users, we also want to make sure that certain endpoints can be called only when users have specific authorizations. In the following example, we want to use our Display OAuth scope.

Enhance spring-security.xml to protect routes with OAuth scopes

The backend itself can be easily adapted based on the spring-security.xml. In this case, we protect the /hello route with our Display OAuth Scope. Introduce (or uncomment) the following line within the <sec:http> element:

<sec:intercept-url pattern="/hello" access="#oauth2.hasScope('${xs.appname}.Display')" method="GET" />

Afterwards you need to redeploy the application with

mvn clean install
cf push

Furthermore, the user accessing the application, needs to be assigned the Display OAuth scope. This is done using the SCP cockpit.

First, go to your trial account on Cloud Foundry and find the role collections menu under the Security module:

Second, create a new role collection which you can give an arbitrary name. In our case, we call the role collection Business Partner Manager.

Afterwards, select the role collection “Business Partner Manager” and select “Add Role”. From the menu, select your application and the corresponding role template and role as shown below:

Afterwards, the user has to be assigned to the newly created Business Partner Manager in order to receive the Display scope. In order to do this, select the trust configuration from the security menu and select the SAP ID Service from the list:

In the opening dialog, enter your User ID as e-mail into the user field and click “Show Assignments” followed by “Add Assignments”:

Select the “Business Partner Manager” role collection from the menu to assign it to your user:
Afterwards you have a route that is protected by the Display OAuth scope which you can still access because the user has now the corresponding role.

That’s it for today. Now you have learned the basics to protect your application on SAP Cloud Platform, CloudFoundry based on the SAP Cloud SDK. Stay tuned for upcoming blog posts about more advanced usages of the SAP Cloud SDK.

Understanding Roles, Role Collections and Scopes

The following picture explains how the various concepts are related to each other.

Gray Box: As a SCP developer (e.g., SAP, partner, customer) of the business application (gray box), you define role templates which may contain multiple OAuth scopes. The developer here define the scope, role templates and additional attributes within the xs-security.json as explained in this tutorial which is used when creating the service instantiation to the XSUAA.

Orange Box: As an SCP tenant administrator of the business application (customer) can create a role collection which is spanning multiple roles reflecting the role templates. This way you can achieve, on the one hand, a fine-granular authorization control for the microservices and, on the other hand, compose them very flexibly in coarse-grained role collections. The idea behind this is, that, for example, the Business Partner Manager role collection may span multiple applications and microservices all having individual scopes. The role collections resolves the roles and scopes and returns a union of all scopes which are composed by the role collection.

Green Box: As an administrator of the users (customer), the role collection can then be assigned to the final user using the SAML attribute “Groups”.
[DONE]

Sometimes it might be necessary to investigate the JWT on the backend microservice during development to check for potential errors. Here is an example Servlet that prints the token out.

@WebServlet("/debug")
public class JwtDebugServlet extends HttpServlet {

    @Override
    protected void doGet(final HttpServletRequest request, final HttpServletResponse response )
            throws ServletException, IOException
    {
        response.setContentType("text/plain");
        Enumeration headerNames = request.getHeaderNames();
        while (headerNames.hasMoreElements()) {
            String key = (String) headerNames.nextElement();
            String value = request.getHeader(key);

            response.getOutputStream().println(key+" : "+value);
        }
    }
}

Afterwards you may use https://jwt.io/ to decode the token. Note: You should never use this with any productive JWT as these tokens are shared on a public website. Fallback to local solutions.

In addition, you may use the XSUAA to see which current scopes and roles a particular users has. You could do this with your XSUAA tenant-specific URL:

https://<tenantId>.authentication.eu10.hana.ondemand.com/config?action=who

which returns something like this:

So far, we have used the XSUAA service itself as the user provider. However, in production scenarios customer’s may want to use their own Identity Provider (IdP) as a user provider or delegate into on-premise user stores such as LDAP or ActiveDirectory. In the following, we quickly show how the XSUAA service can delegate requests to such an external IdPs.

To make this happen, the IdP and the service provider (SP) have to exchange security metadata, i.e., the IdP has to import the metadata of the SP and vice versa.

You can retrieve the metadata from your XSUAA tenant by following the pattern https://.authentication.eu10.hana.ondemand.com/saml/metadata. In my case, that would be https://p1942765239trial.authentication.eu10.hana.ondemand.com/saml/metadata. This downloads the metatdata to your local computer.

Second, you need to import the metadata into your IdP. In the following, we use an own SAP Cloud Identity tenant to do this.

1. Within the IdP, we have to create a new application called MyApp where we select the SAML 2.0 Configuration

2. Import the SP’s metadata and click “Save”.

3. Back in the SCP account cockpit we need to add the IdP’s metadata in the same manner

4. Click “New Trust Configuration” and add the metadata from the IdP and click “Save”