How to add another authorization-filter to a url that is already protected by Keycloak

I have a Spring Boot application protected with KeycloakWebSecurityConfigurerAdapter. Now i want to add another (custom) way of authentication for certain endpoints. Therefore i created a class extending AbstractAuthenticationProcessingFilter and AuthenticationProvider with its custom logic. Now i want to add the custom filter to the HttpSecurity object in my security-configuration with

http.addFilterBefore(new VendorSessionAuthorizationFilter(), KeycloakAuthenticationProcessingFilter.class);

My understanding is that i get to my custom filter first and depending on the result, the security-filter-chain goes on to the Keycloak-Filters. When i test to call an endpoint i never get to the attemptAuthentication method i implemented in my filter. I have the feeling that no matter what i do when calling http.addFilterBefore(... the Keycloak-Filters are always executed so there is no way for me to have another way of authentication.

Here the SecurityConfiguration:

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(jsr250Enabled = true, prePostEnabled = true)
public class KeycloakSecurityConfiguration extends KeycloakWebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        super.configure(http);

        http.addFilterBefore(new VendorSessionAuthorizationFilter(), KeycloakAuthenticationProcessingFilter.class);
        http.authenticationProvider(new VendorSessionAuthenticationProvider());

        http
                .cors().and()
                .csrf().disable()
                .sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS)
                .sessionAuthenticationStrategy(sessionAuthenticationStrategy())
                .and().formLogin().disable()
                .httpBasic().disable()
                .logout().disable()

                .authorizeRequests()
                .anyRequest().authenticated();
    }

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        KeycloakAuthenticationProvider keycloakAuthenticationProvider = keycloakAuthenticationProvider();
        keycloakAuthenticationProvider.setGrantedAuthoritiesMapper(new SimpleAuthorityMapper());
        auth.authenticationProvider(keycloakAuthenticationProvider);
    }

    @Override
    protected SessionAuthenticationStrategy sessionAuthenticationStrategy() {
        return new NullAuthenticatedSessionStrategy();
    }

    @Bean
    public KeycloakConfigResolver KeycloakConfigResolver() {
        return new KeycloakSpringBootConfigResolver();
    }

    @Bean
    public FilterRegistrationBean keycloakAuthenticationProcessingFilterRegistrationBean(
            KeycloakAuthenticationProcessingFilter filter) {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean(filter);
        registrationBean.setEnabled(false);
        return registrationBean;
    }

    @Bean
    public FilterRegistrationBean keycloakPreAuthActionsFilterRegistrationBean(
            KeycloakPreAuthActionsFilter filter) {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean(filter);
        registrationBean.setEnabled(false);
        return registrationBean;
    }

    @Bean
    public FilterRegistrationBean keycloakAuthenticatedActionsFilterBean(
            KeycloakAuthenticatedActionsFilter filter) {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean(filter);
        registrationBean.setEnabled(false);
        return registrationBean;
    }

    @Bean
    public FilterRegistrationBean keycloakSecurityContextRequestFilterBean(
            KeycloakSecurityContextRequestFilter filter) {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean(filter);
        registrationBean.setEnabled(false);
        return registrationBean;
    }
}

```