DelegatingSerializationFilter Could not set ObjectFilter: null warning message is repetitively appearing in console

Use

-Djdk.serialSetFilterAfterRead=true

See the following for more details

https://issues.redhat.com/browse/KEYCLOAK-15901

Seems like the problem is caused by ObjectInputStream.setObjectFilter (on Java 9 - 11) respective ObjectInputStream.setInternalObjectInputFilter (in Java 8) throws IllegalStateException("filter can not be set after an object has been read")

Now I don't see the warnings after I did some changes. This is what I did in my pom.xml and made some changes to the Config class which extends the KeycloakWebSecurityConfigurerAdapter

public class ResourceServerConfig extends KeycloakWebSecurityConfigurerAdapter {

public final KeycloakClientRequestFactory keycloakClientRequestFactory;

// keycloakClientRequestFactory injected via constructor
public ResourceServerConfig(KeycloakClientRequestFactory keycloakClientRequestFactory) {
    this.keycloakClientRequestFactory = keycloakClientRequestFactory;
}

...
...
/**
 * To simplify communication between clients, Keycloak provides an extension of Spring’s RestTemplate that handles
 * bearer token authentication for you. To enable this feature your security configuration must add the
 * KeycloakRestTemplate bean. Note that it must be scoped as a prototype to function correctly.
 * <p>
 * Refer: https://www.keycloak.org/docs/latest/securing_apps/#_spring_security_adapter (Spring Security Adapter)
 *
 * @return
 */
@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
public KeycloakRestTemplate keycloakRestTemplate() {
    return new KeycloakRestTemplate(keycloakClientRequestFactory);
}
}

And in the pom.xml file

        <dependency>
        <groupId>org.keycloak</groupId>
        <artifactId>keycloak-spring-boot-starter</artifactId>
        <version>12.0.4</version>
    </dependency>
    <dependency>
        <groupId>org.keycloak</groupId>
        <artifactId>keycloak-spring-security-adapter</artifactId>
        <version>13.0.1</version>
    </dependency>