Replace removed Reactor context-related operators

[marcusdacoregio]

Related: reactor/reactor-core#2953

[bergerst]

Is there any chance you could merge these changes into 5.7 or 5.8?

The Mono.contextWrite() are part of reactor since 3.4.0, so afaik there should be no problems.

I'm asking because I've updated my project to reactor 3.5.0 and now the ServerWebExchangeReactorContextWebFilter is broken.

java.lang.NoSuchMethodError: 'reactor.core.publisher.Mono reactor.core.publisher.Mono.subscriberContext(reactor.util.context.Context)'
	at org.springframework.security.config.web.server.ServerHttpSecurity$ServerWebExchangeReactorContextWebFilter.filter(ServerHttpSecurity.java:3239)
	at org.springframework.web.server.handler.DefaultWebFilterChain.invokeFilter(DefaultWebFilterChain.java:127)
	at org.springframework.web.server.handler.DefaultWebFilterChain.lambda$filter$0(DefaultWebFilterChain.java:121)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:165)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:129)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:129)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondComplete(MonoFlatMap.java:245)
	at reactor.core.publisher.MonoFlatMap$FlatMapInner.onNext(MonoFlatMap.java:305)
	at reactor.core.publisher.Operators$BaseFluxToMonoOperator.completePossiblyEmpty(Operators.java:2034)
	at reactor.core.publisher.MonoCollectList$MonoCollectListSubscriber.onComplete(MonoCollectList.java:118)
	at reactor.core.publisher.FluxIterable$IterableSubscription.fastPath(FluxIterable.java:362)
	at reactor.core.publisher.FluxIterable$IterableSubscription.request(FluxIterable.java:227)
	at reactor.core.publisher.Operators$BaseFluxToMonoOperator.request(Operators.java:2004)
	at reactor.core.publisher.MonoFlatMap$FlatMapInner.onSubscribe(MonoFlatMap.java:291)
	at reactor.core.publisher.Operators$BaseFluxToMonoOperator.onSubscribe(Operators.java:1988)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:165)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:87)
	at reactor.core.publisher.MonoFromFluxOperator.subscribe(MonoFromFluxOperator.java:81)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:165)
	at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:74)
	at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:82)
	at reactor.core.publisher.FluxFilterWhen$FluxFilterWhenSubscriber.drain(FluxFilterWhen.java:301)
	at reactor.core.publisher.FluxFilterWhen$FluxFilterWhenSubscriber.onNext(FluxFilterWhen.java:140)
	at reactor.core.publisher.FluxIterable$IterableSubscription.slowPath(FluxIterable.java:272)
	at reactor.core.publisher.FluxIterable$IterableSubscription.request(FluxIterable.java:230)
	at reactor.core.publisher.FluxFilterWhen$FluxFilterWhenSubscriber.onSubscribe(FluxFilterWhen.java:200)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:165)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:87)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at org.springframework.cloud.sleuth.instrument.web.TraceWebFilter$MonoWebFilterTrace.subscribe(TraceWebFilter.java:181)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.Mono.subscribeWith(Mono.java:4510)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4411)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4347)
	at org.springframework.test.web.reactive.server.HttpHandlerConnector.lambda$doConnect$2(HttpHandlerConnector.java:98)
	at org.springframework.mock.http.client.reactive.MockClientHttpRequest.lambda$null$2(MockClientHttpRequest.java:124)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.FluxConcatIterable$ConcatIterableSubscriber.onComplete(FluxConcatIterable.java:147)
	at reactor.core.publisher.FluxConcatIterable.subscribe(FluxConcatIterable.java:60)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.Mono.subscribeWith(Mono.java:4510)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4411)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4347)
	at org.springframework.test.web.reactive.server.HttpHandlerConnector.doConnect(HttpHandlerConnector.java:112)
	at org.springframework.test.web.reactive.server.HttpHandlerConnector.lambda$connect$0(HttpHandlerConnector.java:79)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.MonoSubscribeOn$SubscribeOnSubscriber.run(MonoSubscribeOn.java:126)
	at org.springframework.cloud.sleuth.instrument.reactor.ReactorSleuth.lambda$null$6(ReactorSleuth.java:324)
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84)
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)