title: APACHE NIFI invokeHTTP to get token issue
body: <p>I got a secure cluster NIFI with 3 nodes, configured with truststore.jks and keystore.jks</p>
  
  <p>In my invokeHTTP, i've set "StandardSSLContextService" with keystore and trustore for https.</p>
  
  <ul>
  <li><p>invokeHTTP works when i'm trying <a href="https://nifi:9443/nifi-api/controller/config" rel="noreferrer">https://nifi:9443/nifi-api/controller/config</a></p>
  
  <ul>
  <li>but not works when i'm trying "<a href="https://auth_server/oauth/access_token" rel="noreferrer">https://auth_server/oauth/access_token</a>" </li>
  </ul></li>
  </ul>
  
  <p>So when I'm trying use invokeHTTP to get token but it failed with this error :</p>
  
  <pre><code>sun.security.validator.ValidatorException: PKIX path building failed:      
  
  sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
  </code></pre>
  
  <p>thanks for helps</p>