Secure Your Application on SAP Business Technology Platform Cloud Foundry
- How to set up and configure the App Router component as a central entry point to your microservice landscape to handle authentication and authorization
- How to protect your Java microservice so that it only accepts requests based on a valid JSON Web Token (JWT) that is received from the App Router
- Assign roles and scopes to your application users and let your backend deal with authorization information
Prerequisites
- You completed all steps until Create a Sample Application on Cloud Foundry Using SAP Cloud SDK.
- Step 1
Before diving deeper into the real setup of the architecture, let’s quickly review the architecture this tutorial intends to go for.
Figure 1 presents the final setup. First, there still is your existing “Hello World” or “Business Partner” Java-based microservice that you have created in the previous tutorials. However, instead of letting the customer access this application directly, you 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 is 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 requires 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.
- Step 2
You will let Cloud Foundry retrieve the App Router automatically on deployment. To achieve this, you will first set up the necessary structure.
-
Go to your favourite
<destLocation>
and create theapprouter
directory:BashCopycd <destLocation> mkdir approuter cd approuter
-
Place the following
package.json
in yourapprouter
directory:JSONCopy{ "name": "approuter", "dependencies": { "@sap/approuter": "*" }, "scripts": { "start": "node node_modules/@sap/approuter/approuter.js" } }
-
Within
<destLocation>/approuter
create a new file calledxs-app.json
with the following content:JSONCopy{ "welcomeFile": "index.html", "routes": [{ "source": "/", "target": "/", "destination": "app-destination" }] }
-
Last but not least create a new
manifest.yml
file within<destLocation>
for the app router microservice with the following content:YAMLCopy
--- applications: - name: approuter routes: - route: approuter-<subdomain>.cfapps.<region_id>.hana.ondemand.com path: approuter memory: 128M buildpacks: - nodejs_buildpack env: TENANT_HOST_PATTERN: 'approuter-(.*).cfapps.<region_id>.hana.ondemand.com' destinations: '[{"name":"app-destination", "url" :"<APPLICATION_URL>", "forwardAuthToken": true}]' services: - my-xsuaaAdapt the file as follows:
-
Replace
<subdomain>
with your subdomain. You will find your subdomain in the CF cockpit by heading to the overview page of your sub-account: -
Swap out both instances of
<region_id>
with your specific region (e.g.eu10
). You can find it for instance included in the API endpoint (also listed in the image above) just beforehana.ondemand.com
. More details on the region specific URLs can be found here. - In
destinations
replace<APPLICATION_URL>
with the actual URL of your previously deployed app. Again you can find it in the CF cockpit or by listing all existing routes viacf routes
. Note: The URI specified for<APPLICATION_URL>
must be absolute, e.g.https://<app-name>.cfapps.<region>.hana.ondemand.com
.
-
Understanding the AppRouter’s
manifest.yml
On Cloud Foundry every sub-account is assigned exactly one subdomain which is associated to exactly one tenant. In a multi-tenant scenario the app router needs to know which tenant to forward to the XSUAA service. This is achieved by including the subdomain in the host, from which the app router will extract it. That is where the
TENANT_HOST_PATTERN
comes into play. It is a variable that declares the pattern how tenants in the URL are identified and handled. This tutorial expects the host to conform toapprouter-<subdomain>
. If you desire different URL patterns, you need to change theroute
andTENANT_HOST_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. This tutorial series assumes that you want to build multi-tenant applications, as it is aimed towards cloud-native development. However, this variable is not necessary if you have a single-tenant application. To realize this, thexs-security.json
security descriptor may declare"tenant-mode": "dedicated"
(see step 5 below).Moving on to the
destinations
entry. It is a variable that declares the internal routes from the App Router to the underlying backend microservices. As you have only one microservice yet, you may define only one destination calledapp-destination
here. Thisapp-destination
is referenced by the previously createdxs-app.json
file.Last but not least the
services
section declares to bind your own XSUAA service instance to the App Router. This binding will ensure a correspondingVCAP_SERVICES
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:Bind the XSUAA Service
Now you need to create a service binding to the XSUAA service. As a prerequisite you require an
xs-security.json
(security descriptor) file that contains a declaration about authorization scopes you intend to use in your application. For example, simply declare aDISPLAY
scope that will be used later on to authorize your users. In addition, a so-called role template calledViewer
that references yourDISPLAY
scope is declared.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 thexs-security.json
can be found here.The
xsappname
has to be unique within the entire XSUAA instance. We suggest you follow the same pattern of<app-name>-<subdomain>
.As explained above, the
"tenant-mode": "shared"
assumes a multi-tenant application and will require theTENANT_HOST_PATTERN
variable to be declared. You may also use"tenant-mode": "dedicated"
if you develop a single-tenant application.<destLocation>/xs-security.json
:JSONCopy{ "xsappname": "firstapp-<subdomain>", "tenant-mode": "shared", "scopes": [ { "name": "$XSAPPNAME.Display", "description": "display" } ], "role-templates": [ { "name": "Viewer", "description": "Required to view things in your solution", "scope-references" : [ "$XSAPPNAME.Display" ] } ] }
Create the file and change the app name just like before.
Then create a service instance called
my-xsuaa
of the XSUAA service by issuing the following command and using thexs-security.json
file:BashCopycf 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:BashCopycf unbind-service firstapp my-xsuaa cf delete-service my-xsuaa
After you have created the XSUAA service instance, deploy the app router using the following (with the appropriate API endpoint of your Cloud Foundry region):
BashCopycd <destLocation> cf push
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:After logging in you should see the
HelloWorld
servlet which is now served by the App Router as a proxy to your Java application: -
- Step 3
After authentication works with the App Router, your java backend service is still fully visible in the web and not protected. Therefore, you need to protect your java microservices as well so that they accept requests with valid JWTs for the current user only. In addition, you will setup the microservice in a way that it deals with authorization, i.e., understands the OAuth scopes from the JWT that you have configured previously using the
xs-security.json
file.The following steps apply to the
TomEE
runtimes. For Spring please select the relevant tab at the top of this section.In the following, you will use the security capabilities of the SAP Java Buildpack to protect the microservices.
In your
application/src/main/webapp/WEB-INF/web.xml
file, add the following login configuration:XMLCopy<login-config> <auth-method>XSUAA</auth-method> </login-config>
This enables authentication of requests using incoming OAuth authentication tokens.
Additionally make sure that the following
security-constraint
block is contained in yourweb.xml
file:XMLCopy<security-constraint> <web-resource-collection> <web-resource-name>Baseline Security</web-resource-name> <url-pattern>/*</url-pattern> </web-resource-collection> <auth-constraint> <role-name>*</role-name> </auth-constraint> </security-constraint> <security-role> <role-name>Display</role-name> </security-role> <!-- <security-role> <role-name>Further Role Name</role-name> </security-role> -->
That way all endpoints of your application can be accessed by users with any of the role names specified in the
security-role
tags.To specifically secure your endpoints by requiring a specific role you now only need to add an annotation to your endpoint. For your
BusinessPartnerServlet
this looks like this:JavaCopy@ServletSecurity(@HttpConstraint(rolesAllowed = { "Display" })) public class BusinessPartnerServlet extends HttpServlet { // ... }
This will allow only users with the provided role to have access to the annotated endpoint. Compare for this the
xs-security.json
you created earlier to create the XSUAA service.At this point you should now rebuild your application and push it to Cloud Foundry.
BashCopycd /path/to/firstapp/application mvn clean install cd /path/to/firstapp cf push
If you now call the
/businesspartners
endpoint of your application you will see a401
Unauthorized status code, as you were not authorized by the App Router. Calling the/businesspartners
endpoint via your App Router on the other hand will give you a403
Forbidden status code meaning that you do not have the necessary authorization to see this page. This is to be expected, as you secured the endpoint with the annotation above without assigning the requested roleDisplay
to your user. You will fix this in the next step. - Step 4
To regain access to your secured endpoint, you need to get the
Display
OAuth scope assigned. This is done using the BTP cockpit.-
First, go to your 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. For example, you might call the role collection Business Partner Manager.
- Afterwards, select the role collection Business Partner Manager, select Edit, and add a new role. From the menu, select your application and the corresponding role template and role. Finish up the process by adding the newly created role and saving the Business Partner Manager role collection.
-
Afterwards, the user has to be assigned to the newly created Business Partner Manager in order to receive the Display scope. To do this, select Users from the security menu and select the user that should receive the permissions from the list.
-
On the right hand side, under the Role Collections headline, select Assign Role Collection and choose the Business Partner Manager collection. Confirm the selection by clicking on the Assign Role Collection button.
Afterwards you have the
Display
OAuth scope assigned to your user, which allows you to access the secured endpoints again. -
- Step 5
Now you are ready to build and deploy the application to try all your changes with:
BashCopycd /path/to/firstapp/application mvn clean install cd /path/to/firstapp cf push
After deployment, accessing your backend service directly should not be possible anymore and result in the following message:
However, you should still be able to access your application using the App Router as entry point:
- Step 6
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, you should remove it. For this remove the following lines from yourweb.xml
:XMLCopy<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>
- Step 7
The following picture explains how the various concepts are related to each other.
Gray Box: As a BTP 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 BTP tenant administrator of the business application (customer), you 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), you can assign the role collection to the final user using the SAML attribute
Groups
. - Step 8
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.
JavaCopy@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. - Step 9
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://<subdomain>.authentication.<region_id>.hana.ondemand.com/config?action=who
- Step 10
So far, you 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 Active Directory. The following paragraphs quickly explain 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://<subdomain>.authentication.<region_id>.hana.ondemand.com/saml/metadata
, e.g.https://p123456trial.authentication.eu10.hana.ondemand.com/saml/metadata
. This downloads the metadata as an XML file.Secondly, you need to import the metadata into your IdP. In the following example, a SAP Cloud Identity tenant is used.
-
Within the IdP, you have to create a new application called
MyApp
where you select the SAML 2.0 Configuration. -
Import the SP’s metadata and click Save.
-
Back in the BTP account cockpit you need to add the IdP’s metadata in the same manner.
-
Click New Trust Configuration and add the metadata from the IdP and click Save.
-
- Step 11
In terms of OAuth 2.0, what role does the Authorization and Trust Management (xsuaa) service play in the application security setup?
- Step 12
Which of the following authorization artifacts of applications running in the Cloud Foundry environment on SAP Cloud Platform can be specified at the application design time?
- Concepts
- Set up the App Router
- Protect your backend microservice
- Assign users to scopes
- Deploy and test the application
- Remove CSRF token protection from backing service
- Understanding Roles, Role Collections and Scopes
- Troubleshoot JSON Web Tokens
- Troubleshoot OAuth scopes from XSUAA
- Set up your own identity provider
- Test yourself
- Test yourself