using webflux in the controllers breaks mvc spring security SecurityFilterChain

[dev-wealthpilot]

Describe the bug
Some of the controllers return a ResponseEntity<Flux<...>> object. This makes the whole call asynchronous which then leads to the problem that the SecurityFilterChain loses the authentication information.
Normally this is mitigated by enabling @EnableWebFluxSecurity - but this breaks mvc applications.

To Reproduce
Steps to reproduce the behavior:

use mvc application and create SecurityFilterChain that requires login, then try to protect ff4j REST calls

    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http
        ...configure authentication 
        .authorizeHttpRequests(authorize -> authorize
                                        ...
                                        .requestMatchers("/api/ff4j/**").hasAuthority("ROLE_ADMIN")
                                        ...
                                        );

Expected behavior
when logged in with ROLE_ADMIN then access to /api/ff4j/** should be granted.
Actual behaviour is that access is always denied because of webflux usage in the ff4j rest apis

this worked in pre 2.x versions