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

[[_saml_multi_tenancy]]
==== Multi Tenancy

SAML offers the same functionality as OIDC for <<_multi_tenancy,Multi Tenancy>>, meaning that a single target application (WAR) can be secured with multiple {project_name} realms. The realms can be located on the same {project_name} instance or on different instances.

To do this, the application must have multiple `keycloak-saml.xml` adapter configuration files.

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

{project_name} makes it possible to have a custom config resolver, so you can choose which adapter config is used for each request. In SAML, the configuration is only interesting in the login processing; once the user is logged in, the session is authenticated and it does not matter if the `keycloak-saml.xml` returned is different. For that reason, returning the same configuration for the same session is the correct way to go.

To achieve this, create an implementation of `org.keycloak.adapters.saml.SamlConfigResolver`. The following example uses the `Host` header to locate the proper configuration and load it and the associated elements from the applications' Java classpath:

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

import java.io.InputStream;
import org.keycloak.adapters.saml.SamlConfigResolver;
import org.keycloak.adapters.saml.SamlDeployment;
import org.keycloak.adapters.saml.config.parsers.DeploymentBuilder;
import org.keycloak.adapters.saml.config.parsers.ResourceLoader;
import org.keycloak.adapters.spi.HttpFacade;
import org.keycloak.saml.common.exceptions.ParsingException;

public class SamlMultiTenantResolver implements SamlConfigResolver {

    @Override
    public SamlDeployment resolve(HttpFacade.Request request) {
        String host = request.getHeader("Host");
        String realm = null;
        if (host.contains("tenant1")) {
            realm = "tenant1";
        } else if (host.contains("tenant2")) {
            realm = "tenant2";
        } else {
            throw new IllegalStateException("Not able to guess the keycloak-saml.xml to load");
        }

        InputStream is = getClass().getResourceAsStream("/" + realm + "-keycloak-saml.xml");
        if (is == null) {
            throw new IllegalStateException("Not able to find the file /" + realm + "-keycloak-saml.xml");
        }

        ResourceLoader loader = new ResourceLoader() {
            @Override
            public InputStream getResourceAsStream(String path) {
                return getClass().getResourceAsStream(path);
            }
        };
        
        try {
            return new DeploymentBuilder().build(is, loader);
        } catch (ParsingException e) {
            throw new IllegalStateException("Cannot load SAML deployment", e);
        }
    }
}
----

You must also configure which `SamlConfigResolver` 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.SamlMultiTenantResolver</param-value>
    </context-param>
</web-app>
----