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Destination Cache and Isolation

The SAP Cloud SDK provides the option to cache destinations for efficiency reasons. Cached destination need to be isolated to the correct users.

This guide explains the different options for destination caching with the SAP Cloud SDK. The general destination lookup is described in this guide.

Destination Service Cache​

To reduce the number of calls to the destination service, you can enable the destination cache. All the discussed options apply to the execute() and getDestination() methods of the SAP Cloud SDK. The destination caching is disabled by default. Setting the useCache flag to true enables it:

.execute({ destinationName: 'myDestination', jwt: '<JWT>', useCache: true })

A cached destination is stored for 5 minutes in the cache. The SAP Cloud SDK tries to set the proper isolation strategy for the destination automatically. There are two options:

  • Tenant: The destination is cached for a tenant and different users will hit the same cache entry.
  • TenantUser: The destination is cached separately for each user of a tenant.

The SAP Cloud SDK sets the isolation based on the provided JWT:

  • No JWT: Isolation is set to Tenant and value for the tenant is the provider account.
  • JWT without user_id: Isolation is set to Tenant and the value for the tenant is the zid of the JWT.
  • JWT with user_id: Isolation is set to TenantUser and values are taken from zid and user_id.

This is a safe choice which prevents privilege escalation due to caching. The first two cases are typical for user-independent authentication flows. Examples of such a flow are BasicAuthentication, ClientCertificateAuthentication or OAuth2ClientCredentials.

There are cases where the choice made by the SAP Cloud SDK is not optimal. Assume you have a multi-tenant scenario and you need to pass the JWT to obtain the destination for the right tenant.

The JWT contains a user_id but the destination flow is user-independent. The SAP Cloud SDK would use isolation TenantUser, although Tenant would be sufficient.

In such a case, you can manually enforce weaker isolation:

.execute({
  destinationName: 'myDestination',
  jwt: 'yourJWT',
  isolationStrategy: IsolationStrategy.Tenant
})
caution

Be very careful with this option. You should know what you're doing when manually downgrading the isolation strategy from TenantUser level. An erroneous configuration can have severe consequences like privilege escalation between users.

Custom Destination Service Cache​

When the cache option is enabled, the SAP Cloud SDK stores the fetched destinations in an in-memory cache. However, in certain cases, a persistent or distributed cache may be more suitable according to your application architecture.

To create your custom destination cache provider, implement the DestinationCacheInterface interface shown below and define the get, set, and clear methods.

export interface DestinationCacheInterface {
  hasKey(key: string): Promise<boolean>;
  get(key: string | undefined): Promise<Destination | undefined>;
  set(key: string | undefined, item: CacheEntry<Destination>): Promise<void>;
  clear(): Promise<void>;
}

Note that each item in the cache is represented using the type CacheEntry<T> which defines two properties:

  • entry, the item you want to store, and
  • expires, the expiration time for an individual cache item, this is optional.

Once you have implemented your custom cache provider, you can tell the SAP Cloud SDK to use it in place of the default one. Pass your custom destination cache provider to the setDestinationCache() method before the first calls to either the getDestination() or the generic client's executeHttpRequest() function.

class CustomCacheProvide implements DestinationCacheInterface {
  // your custom implementation
}

setDestinationCache(new CustomCacheProvider());

All subsequent calls to fetch destinations will use the custom cache.

Register Destination Cache​

The registerDestination() function is like a manual cache for destinations. This function behaves similarly to the destination service cache discussed above. The destination lookup guide explains the usage of this function in more detail.

import { registerDestination } from '@sap-cloud-sdk/connectivity';

const destination = {
  name: 'FORWARD-DESTINATION',
  url: 'https://mys4hana.com'
};

registerDestination(destination, { jwt: 'yourJWT' });

The isolation strategy is automatically detected and applied based on the given JWT:

  • No JWT: Isolation is set to Tenant and value for the tenant is the provider account.
  • JWT without user_id: Isolation is set to Tenant and the value for the tenant is the zid of the JWT.
  • JWT with user_id: Isolation is set to TenantUser and values are taken from zid and user_id.

You can override the automatically detected isolation strategy.

registerDestination(destination, {
  jwt: 'yourJWT',
  isolationStrategy: IsolationStrategy.Tenant
});