keycloak-scim/securing_apps/topics/oidc/java/multi-tenancy.adoc

==== Multi Tenancy

Multi Tenancy, in our context, means that a single target application (WAR) can be secured with multiple {{book.project.name}} realms. The realms can be located
one the same {{book.project.name}} instance or on different instances.

In practice, this means that the application needs to have multiple `keycloak.json` adapter configuration files.

You could have multiple instances of your WAR with different adapter configuration files deployed to different context-paths. However, this may be inconvenient
and you may also want to select the realm based on something else than context-path.

{{book.project.name}} makes it possible to have a custom config resolver so you can choose what adapter config is used for each request.

To achieve this first you need to create an implementation of `org.keycloak.adapters.KeycloakConfigResolver`. For example:

[source,java]
----
package example;

import org.keycloak.adapters.KeycloakConfigResolver;
import org.keycloak.adapters.KeycloakDeployment;
import org.keycloak.adapters.KeycloakDeploymentBuilder;

public class PathBasedKeycloakConfigResolver implements KeycloakConfigResolver {

    @Override
    public KeycloakDeployment resolve(OIDCHttpFacade.Request request) {
        if (path.startsWith("alternative")) {
            KeycloakDeployment deployment = cache.get(realm);
            if (null == deployment) {
                InputStream is = getClass().getResourceAsStream("/tenant1-keycloak.json");
                return KeycloakDeploymentBuilder.build(is);
            }
        } else {
            InputStream is = getClass().getResourceAsStream("/default-keycloak.json");
            return KeycloakDeploymentBuilder.build(is);
        }
    }

}
----

You also need to configure which `KeycloakConfigResolver` implementation to use with the `keycloak.config.resolver` context-param in your `web.xml`:

[source,xml]
----
<web-app>
    ...
    <context-param>
        <param-name>keycloak.config.resolver</param-name>
        <param-value>example.PathBasedKeycloakConfigResolver</param-value>
    </context-param>
</web-app>
----