title: iOS verify certificate by CA locally
body: <p>My app contains a public certificate (cert A) that is used for https connection. It works by using this method <code>URLSession:didReceiveChallenge:completionHandler:</code> 
  But I would like to verify certificate (cert B) that is downloaded with additional data from server. Cert A is CA for cert B. 
  I cant find any solutions. </p>
  
  <p>I use X.509 standard. (cert A is .pfx and cert B is .der)</p>