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Author's profile photo Alessandro Biagi

Extend SAP SuccessFactors on SAP BTP with CAP – Add Security

Prerequisites

To follow-up with this blog post you must have read and completed the following previous blog posts in this series:

Define Authorizations

So far, we have been working on a local project which only developers would have access to. Therefore, it’s OK to leave our service “unprotected” as it’s not yet publicly available. But, as soon as we deploy it to the cloud, it will be available to anyone who knows the service endpoint (which is not quite difficult).

In such scenario, anyone can access the service anonymously and freely make OData calls to it, which will probably cause a big mess in our application and related data. So, it’s imperative to “protect” our service against such risky situation by granting access only to authenticated users.

Then, to make the service available only to authenticated users, we just need to add the requires annotation to the service definition (in the projman-service.cds file), like demonstrated below:

Figure%201%20-%20Annotation%20for%20requiring%20the%20user%20to%20be%20authenticated

Figure 1 – Annotation for requiring the user to be authenticated

Now, in the service home page, when we click on any entity link (i.e. SFSF_User) a pop-up in the browser will ask for the username and password.

Figure%202%20-%20Login%20pop-up%20for%20mocked%20authentication

Figure 2 – Login pop-up for mocked authentication

As we are still in development we can provide whatever information we like and click sign in, because in this environment CAP is using what we call mocked authentication which does not utilize real users. So, after clicking sign in, you may see the data from the selected entity:

Figure%203%20-%20Data%20retrieved%20after%20sign%20in

Figure 3 – Data retrieved after sign in

But, in an administrative scenario like this one, just being an authenticated user is not enough. It’s appropriate that, additionally, the authenticated user must be granted some administrative role (i.e. an Admin role).

Therefore, we need to specify that the entities from our service are only viewable and maintainable by users with the Admin role. To do so, we also annotate our entities with the requires annotation, but now we specify the Admin role, instead of “authenticated-user”, like demonstrated below:

Figure%204%20-%20Restricting%20access%20to%20service%20entities%20for%20the%20Admin%20role

Figure 4 – Restricting access to service entities for the Admin role

Now, if we click again on the same entity link (i.e. SFS_User) we should receive an HTTP 403 (Forbidden) error:

Figure%205%20-%20Unauthorized%20Access

Figure 5 – Unauthorized Access

It happened because the mocked user (any dummy data you provided) was not granted the Admin role, thus cannot access any entity annotated as such.

So, let’s fix it now. To do so, we just need to add an “auth” block into the cds.requires section of the package.json file, like demonstrated below:

Figure%206%20-%20Authorization%20config%20for%20development

Figure 6 – Authorization config for development

This block instructs CAP to use the mock strategy (which is default) during development and it creates two mock users: john who’s granted the Admin role and mary who’s granted the Viewer role (which has no authorization in the context of our application).

Now, we need to login as john (with any password that you like), but CAP has already opened a session to the first mock user we utilized (who has no Admin role granted) and won’t pop-up for a new login (so, we stick with the forbidden error).

To work this around, you will need to completely close your browser (not only the Business Application Studio tab), open it again and go back to your SAP BTP cockpit to access Business Application Studio from the Instances and Subscriptions page. Click on your Dev Space and when the IDE loads again make sure that cds watch is properly running, if not, run it again. Launch the service home page and click any entity link (i.e. SFSF_User).

This time the sign in pop-up should appear and you must login with john to overcome the forbidden error:

Figure%207%20-%20Entity%20data%20successfully%20retrieved%20after%20login%20with%20Admin%20role

Figure 7 – Entity data successfully retrieved after login with Admin role

To learn more about authentication and authorization in CAP, you can refer to this two links from the official documentation:

Prepare Security Setup for Deployment

OK, so far we have defined a simple authorization schema to secure all service entities and verified that it’s working as expected. But, in production, security will be handled by the User Account and Authentication (UAA) mechanism of Cloud Foundry which, in SAP BTP, is implemented by the XSUAA service.

Therefore, we need to configure the XSUAA service instance to recognize and apply the schema we have defined when the application is deployed on SAP BTP.

For that, we need to create a file named xs-security.json in the project root folder, and  the good news is that CAP can do it for us automatically based on the security schema from the service definition.

1. In the Terminal press CTRL+C to terminate the cds watch command, then type the command:

cds compile srv/ --to xsuaa >xs-security.json

Then, press Enter

Figure%208%20-%20xs-security.json%20creation

Figure 8 – xs-security.json creation

2. On the left-hand pane click on the xs-security.json file to open it. Examine the contents and add the two lines indicated in the screenshot below right before “scopes” (if not already generated by the compiler, as older versions of it used to add them automatically). In the role-templates collection, change the description of the Admin role from “generated” to “Project Administrator“:

Figure 9 – Security descriptor content

This file is used during the creation or update of the XSUAA service instance and controls the roles, scopes, attributes and role templates that will be part of the security for your application.

Let’s quickly understand what’s done in this descriptor.

Basically, we define a scope named Admin for the application and assign it to the Admin role template. This way, when the application is deployed to SAP BTP the Admin role will be automatically created in the platform and associated to the sfsf-projman application.

But roles are not directly assigned to the application’s users. The assignment is done through role collections. So let’s just add one to the file like demonstrated in the screenshot below:

Figure%2010%20-%20Create%20Role%20Collection

Figure 10 – Create Role Collection

After deployment, we just need to assign it to the user who should be granted such authorization.

Add Additional Dependencies

Now, we just need to add four dependencies to the CAP service tor it to properly handle security and other related stuff – such as the user JSON Web Token (JWT) – during runtime. Those are:

  • @sap/cds-dk
  • @sap/xsenv
  • @sap/xssec
  • passport
Therefore, ih the Terminal, just type the following commands pressing Enter after each one:
  • npm install @sap/cds-dk
  • npm install @sap/xsenv
  • npm install @sap/xssec
  • npm install passport
When the commands complete, your package.json file should like like the screenshot below:
Figure%2011%20-%20Installed%20dependencies

Figure 11 – Installed dependencies

Conclusion

After having gone through the steps of this blog post you should have successfully secured your CAP application to be viewable and maintainable only by users with administration authorization. Now you are ready to start the steps to deploy it to SAP BTP. The next step is to deploy the application’s data model to an SAP HANA Cloud database.

NOTE: all the instructions provided in this blog post apply exactly the same to any CAP project that should have security applied to its services.

Please, do not hesitate to submit your questions in SAP Community through the Q&A tag link: https://answers.sap.com/index.html

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