title: Peer certificate cannot be authenticated with known CA certificates using PHP OAuth extension
body: <p>I'm using PHP OAuth extension to make a call to the Tradeking API. When I make the exact call as in here, <a href="https://developers.tradeking.com/documentation/php" rel="noreferrer">https://developers.tradeking.com/documentation/php</a></p>
  
  <p>I'm getting the exception </p>
  
  <blockquote>
    <p>Exception caught! Response: making the request failed (Peer certificate cannot be authenticated with known CA certificates)</p>
  </blockquote>
  
  <p>Why this is happening and how can I resolve this?</p>