title: Pass a context from one flux/mono to another
body: <p>Interesting things happen inside the webflux package. However, my journey in the source didn't solve the following question. </p>
  
  <p>Let's say I have the following mono (or flux):</p>
  
  <pre><code>Mono hello = Mono.empty()
              .subscriberContext(ctx -&gt; ctx.put("message", "hello"));
  </code></pre>
  
  <p>I use similar construct within a webfilter to enrich the pipeline with tenant and user data. Then in a controller a construct like this is used:</p>
  
  <pre><code>Mono world = Mono.subscriberContext()
              .map(ctx -&gt; (String)ctx.get("message"));
  </code></pre>
  
  <p>The context of the hello mono is filled in the world mono. I tried to figure out how this is done, also for unit testing purposes. </p>
  
  <p>In the end it remains a riddle. I tried to do this with the regular methods available on both mono/flux objects but I don't succeed in making the hello context available to the world mono. How can you fuse fluxes and monos and passing the context along the way to the upstream operators?</p>