title: How to add a trusted certificate to HTTPPoison/hackney?
body: <p>When I try:</p>
  
  <pre><code>HTTPoison.get! "https://facebook.com"
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code>** (HTTPoison.Error) {:tls_alert, 'unknown ca'}
  [error] SSL: :certify: ssl_handshake.erl:1606:Fatal error: unknown ca
  
      (httpoison) lib/httpoison.ex:66: HTTPoison.request!/5
  </code></pre>
  
  <p>which is kind of expected since in my company I need to trust the firewall's certificate to get out.</p>
  
  <p>I have trusted the certificate (.cer file) system wide, which is why <code>wget</code> doesn't give me ssl errors when accessing <code>https</code> URLs. But it seems that hackney/HTTPoison ignores this configuration.</p>
  
  <p>How to I make HTTPoison/hackney recognize the certificate as a trusted certificate?</p>