title: R / Shiny promises and futures not working with httr
body: <p>I am working in a Shiny app that connects to Comscore using their API. Any attempt at executing POST commands inside future/promises fails with the cryptic error:</p>
  
  <pre><code>Warning: Error in curl::curl_fetch_memory: Bulk data encryption algorithm failed in selected cipher suite.
  </code></pre>
  
  <p>This happens with any POST attempt, not only when/if I try to call Comscore´s servers. As an example of a simple, harmless and uncomplicated POST request that fails, here is one:</p>
  
  <pre><code>rubbish &lt;- future(POST('https://appsilon.com/an-example-of-how-to-use-the-new-r-promises-package/'))
  print(value(rubbish))
  </code></pre>
  
  <p>But everything works fine if I don not use futures/promises.</p>
  
  <p>The problem I want to solve is that currently we have an app that works fine in a single user environment, but it must be upgraded for a multiuser scenario to be served by a dedicated Shiny Server machine. The app makes several such calls in a row (from a few dozen to some hundreds), taking from 5 to 15 minutes.</p>
  
  <p>The code is running inside an observeEvent block, triggered by a button clicked by the user when he has configured the request to be submitted.</p>
  
  <p>My actual code is longer, and there are other lines both before and after the POST command in order to prepare the request and then process the received answer.</p>
  
  <p>I have verified that all lines before the POST command get executed, so the problem seems to be there, in the attempt to do a POST connecting to the outside world from inside a promise.</p>
  
  <p>I am using RStudio Server 1.1.453 along with R 3.5.0 in a RHEL server.
  Package versions are</p>
  
  <ul>
  <li>shiny: 1.1.0</li>
  <li>httr: 1.3.1</li>
  <li>future; 1.9.0</li>
  <li>promise: 1.0.1</li>
  </ul>
  
  <p>Thanks in advance,</p>