Problem description
For certain use cases, I would like to use the embedded Infinispan instance in Keycloak to add own caches used by a external provider, particularly when running Keycloak in cluster mode.

Keycloak already exposes the InfinispanConnectionProvider SPI, which provides access to the Infinispan CacheManager. With the introduction of the new Infinispan configuration SPI (see #37912), it is now possible to contribute cache configurations via the CacheEmbeddedConfigProvider. However, there is no example or test case provided to demonstrate how to use the new SPI.

From what I understand, the intended approach for adding custom caches is to provide cache configurations through an external cache configuration file. However, for some scenarios this is not ideal.

Possible approaches that come to mind are:

• Bundling cache configuration files inside the provider JAR and loading them automatically, or
• Programmatically defining default cache configurations from the provider itself

Current analysis
I experimented with defining a cache configuration programmatically via the CacheEmbeddedConfigProvider:

@Override
public void postInit(KeycloakSessionFactory factory) {
    try (KeycloakSession session = factory.create()) {
        this.defineCacheConfig(session);

        InfinispanConnectionProvider connections = session.getProvider(InfinispanConnectionProvider.class);
        this.cache = connections.getCache(CACHE_ID, true);
        if (this.cache == null) {
            throw new RuntimeException("Failed to get cache instance");
        }
    }

    super.postInit(factory);
}

private void defineCacheConfig(KeycloakSession session) {
    CacheEmbeddedConfigProvider provider = session.getProvider(CacheEmbeddedConfigProvider.class);
    provider.configuration()
            .newConfigurationBuilder(CACHE_ID)
            .clustering()
            .cacheMode(CacheMode.DIST_SYNC);
}

However, when I try to add new cache configurations from a custom provider during the postInit process at the provider factory, it doesn't work as expected.

At that point in the lifecycle:

• The ConfigurationBuilderHolder has already been initialised into the DefaultCacheManager during the migration process at startup.
• Newly added cache configurations from CacheEmbeddedConfigProvider are no longer picked up.

What is the intended and supported way for a custom provider to define new Infinispan caches:

• before the DefaultCacheManager is created,
• without extending or overriding CacheEmbeddedConfigProvider,
• and how can this be done without causing conflicts when multiple providers want to register their own caches?

Call stack from the initialization of the DefaultCacheManager: