PKCE for confidential clients in Spring 5 (non-reactive)

I'm trying to enable PKCE on an oAuth client in Spring Boot 5. The examples I can find are for reactive client, looking something like this:

SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http,    ReactiveClientRegistrationRepository clientRegistrationRepository) {
        DefaultServerOAuth2AuthorizationRequestResolver pkceResolver = new DefaultServerOAuth2AuthorizationRequestResolver(clientRegistrationRepository);
        pkceResolver.setAuthorizationRequestCustomizer(OAuth2AuthorizationRequestCustomizers.withPkce());

http.oauth2Login(login -> login
    .authorizationRequestResolver(pkceResolver)

I tried converting this to the servlet equivalent, but the oAuthLoginConfigurer for that doesn't have an authorizationRequestResolver method to set the PKCE resolver.

This is where I got to:

  @Bean
  public SecurityFilterChain filterChain(HttpSecurity http
          ,ClientRegistrationRepository repo
  ) 
  throws Exception {

    var resolver = new DefaultOAuth2AuthorizationRequestResolver(repo,"https://myoauthserver.com");
    resolver.setAuthorizationRequestCustomizer(OAuth2AuthorizationRequestCustomizers.withPkce());
    
    http
        .authorizeRequests(a -> a
            .antMatchers("/").permitAll()
            .anyRequest().authenticated())
        .oauth2Login(); // doesn't have the authorizationRequestResolver method like reactive



    return http.build();
  }

Any ideas how to make this work for servlet?

Solution

Ok, I've figured out and thought I'd better not leave this question hanging for poor souls in the future (ie. me when I forget how it works).

Here is the magic bean:

@Configuration
public class SecurityConfiguration {

  @Bean
  public SecurityFilterChain filterChain(HttpSecurity http, ClientRegistrationRepository repo)
      throws Exception {

    var base_uri = OAuth2AuthorizationRequestRedirectFilter.DEFAULT_AUTHORIZATION_REQUEST_BASE_URI;
    var resolver = new DefaultOAuth2AuthorizationRequestResolver(repo, base_uri);

    resolver.setAuthorizationRequestCustomizer(OAuth2AuthorizationRequestCustomizers.withPkce());

    http
        .authorizeRequests(a -> a
            .antMatchers("/").permitAll()
            .anyRequest().authenticated())
        .oauth2Login(login -> login.authorizationEndpoint().authorizationRequestResolver(resolver));

    http.logout(logout -> logout
        .logoutSuccessUrl("/"));

    return http.build();
  }
}