我通过使用filterChain来解决这个问题，就像@Elyobek建议的那样，但是代码如下：

@Bean
public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
    http.authenticationProvider(inMemoryAuthenticationProvider);
    http.authenticationProvider(ldapAuthenticationProvider);
    http.userDetailsService(userDetailsService);
}

我没有意识到我可以在HttpSecurity上设置AuthenticationProviders和UserDetailsService。

不如这样吧：

@Configuration
    public class SecurityConfig {

        private AuthenticationManagerBuilder authBuilder;

        public SecurityConfig(AuthenticationManagerBuilder authBuilder) {
            this.authBuilder = authBuilder;
        }

        @Bean
        public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
            authBuilder.authenticationProvider(inMemoryAuthenticationProvider);
            authBuilder.authenticationProvider(ldapAuthenticationProvider);
            authBuilder.userDetailsService(userDetailsService);

            http
                    .authorizeHttpRequests((authz) -> authz
                            .anyRequest().authenticated()
                    )
                    .authenticationManager(authBuilder.getOrBuild())
                   .httpBasic(withDefaults());
            return http.build();
        }
    }