(fixed per discussion/clarification on the correct usage)

Yep: my problem was that I had no control on the authenticator Thank you again !

no problem, reasoning about mixing blocking and non-blocking code is hard and can be counterintuitive, so I hope that I could help in that regard. I'll close this issue, then.

Well, thanks for your time & help Simon!

It is more complex than that. You are dealing with multiple asynchronous streams that have complex interactions and you throw threading/synchronization problems into the mix. This can cause race conditions, dealocks/livelocks, etc...

Blocking inside a map/flatmap is regarded as a malpractice in the Rx world, and if you absolutely must call blocking code you have to switch to proper threads using Schedulers.io() or Schedulers.newThread().

We made a reminder note of absolutely avoiding that in the documentation (granted this can be easily missed, but see second note in http://developer.couchbase.com/documentation/server/4.0/sdks/java-2.2/observables.html#story-h2-5).