Spring Webflux: Read request-body in ServerWebExchangeMatcher - spring-boot

Question

I have to create an application with just one endpoint where users can log in and do their other operational stuff. Users should be able to log in with a request body like:
{
"login": {
"token": "12345"
}
}
So every request with a body like this should be allowed via .permitAll() by the WebFilterChain.
The chain is configured like this:
#Bean
public SecurityWebFilterChain chain(ServerHttpSecurity http) {
return http.authorizeExchange(exchanges -> {
exchanges.matchers(new LoginRequestMatcher())
.permitAll()
.pathMatchers("api/v1*")
.hasRole("USER");
})
.csrf()
.disable()
.build();
}
The LoginRequestMatcher analyzes the body of the request and returns a Match if the pattern is ok. So far, this works quite fine.
My problem is that later in the Controller, the request body can not be accessed any more, so I'm currently trying to put it into a cache or the context to be able to access it later on.
Here is my current implementation of the LoginRequestMatcher:
public class LoginRequestMatcher implements ServerWebExchangeMatcher {
private static final Pattern loginRequestPattern = Pattern.compile("...loginPattern");
#Override
public Mono<MatchResult> matches(final ServerWebExchange exchange) {
return exchange.getRequest().getBody()
.map(dataBuffer -> {
byte[] byteArray=new byte[dataBuffer.readableByteCount()];
dataBuffer.read(byteArray);
DataBufferUtils.release(dataBuffer);
return byteArray;
}).defaultIfEmpty(new byte[0])
.map(bytes -> {
ServerHttpRequestDecorator decorator = initDecorator(exchange, bytes);
exchange.mutate().request(decorator).build();
Mono.just(decorator).contextWrite(ctx -> ctx.put("decorator",decorator))
return decorator;
}
)
// Rest of the code checks for Regex in the body and works fine.
.next();
Now, when I try to get the cached request-body after the RequestMatcher is processed (f.e. in a WebFilter), the context does not contain an object with the key "decorator".
#Configuration
#ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
public class HttpRequestBodyCachingFilter implements WebFilter {
#Override
public Mono<Void> filter(final ServerWebExchange exchange, final WebFilterChain chain) {
final HttpMethod method = exchange.getRequest().getMethod();
// Nothing to cache for GET and DELETE
if (method==null || HttpMethod.GET==method || HttpMethod.DELETE==method) {
return chain.filter(exchange);
}
// Get decorator from context
return Mono.just(exchange)
//ctx.get("decorator") throws Exception here, because the key does not exist.
.flatMap(s -> Mono.deferContextual(ctx -> ctx.get("decorator")))
.map(decorator ->
(ServerHttpRequestDecorator) decorator)
.flatMap(decorator -> chain.filter(exchange.mutate().request(decorator).build()));
}
}
How can I make the body readable after accessing it in inside a ServerWebExchangeMatcher?