Endpoint filters should be reachable when using `spring.mvc.servlet.path`

Expected Behavior

DefaultLoginPageGeneratingFilter supports manual path prefix, such as ${spring.mvc.servlet.path} prefix.

As the issue #14188 that I submitted, DefaultLoginPageGeneratingFilter doesn't work while ${spring.mvc.servlet.path} property is not '/'. due to DefaultLoginPageGeneratingFilter only process fixed url path: /login.

My current solution is to hack FormLoginConfigurer class, like bellow codes:

@Bean
SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception
{
    // Management ENdpoints Base Path is '/__admin'
    String endpointsWebBasePath = AppConfigHolder.getManagementEndpointsBasePath();
    
    if(GeneralHelper.isStrEmpty(endpointsWebBasePath) || endpointsWebBasePath.equals("/"))
        http.authorizeHttpRequests((authorizeHttpRequests) -> authorizeHttpRequests.anyRequest().permitAll()).build();
    else
    {
        // Spring MVC Servlet Path is '/aaa'
        String mvcServletPath = AppConfigHolder.getSpringMvcServletPath();
        // prefix == '/aaa'
        String prefix = (GeneralHelper.isStrNotEmpty(mvcServletPath) && !mvcServletPath.equals("/")) ? mvcServletPath : "";
        // managementBasePath == "/aaa/__admin/**"
        String managementBasePath = prefix + endpointsWebBasePath + "/**";
        
        http
        .authorizeHttpRequests((authorizeHttpRequests) -> authorizeHttpRequests
            .requestMatchers(AntPathRequestMatcher.antMatcher(managementBasePath)).authenticated()
            .requestMatchers(AntPathRequestMatcher.antMatcher("/**")).permitAll())
        .csrf((csrf) -> csrf.disable())
        .httpBasic(Customizer.withDefaults())
        .formLogin(new Customizer<FormLoginConfigurer<HttpSecurity>>()
        {
            @Override
            public void customize(FormLoginConfigurer<HttpSecurity> cfg)
            {
                if(GeneralHelper.isStrEmpty(prefix))
                    return;
				
                // if prefix == '/aaa', then set login page to '/aaa/login'
                cfg.loginPage(prefix + DefaultLoginPageGeneratingFilter.DEFAULT_LOGIN_PAGE_URL);
                
                try
                {
                    final String FIELD_NAME = "customLoginPage";
                    Field customLoginPage   = AbstractAuthenticationFilterConfigurer.class.getDeclaredField(FIELD_NAME);
                    
                    // Because loginPage() set the field 'customLoginPage' of FormLoginConfigurer to true automatically, DefaultLoginPageGeneratingFilter would be ignored.  
                    // Cheat FormLoginConfigurer and reset it's 'customLoginPage' to false.
                    // Ugly, but work fine.
                    customLoginPage.setAccessible(true);
                    customLoginPage.set(cfg, false);
                }
                catch(Exception e)
                {
                    throw new RuntimeException("set actuator login page fail", e);
                }
            }
        });
    }
    
    return http.build();
}

Conclusion

FormLoginConfigurer provides another loginPage() like loginPage(String loginPage, boolean customLoginPage) to replace the hack code above, and then DefaultLoginPageGeneratingFilter would supports manual path prefix.