title: How to fix curl_exec returns false
body: <p>I am developing payment with PHP for weixin.
  The code that I implemented as follow.
  But curl_exec return false and </p>
  
  <pre><code>    $ch = curl_init();
      curl_setopt($ch, CURLOPT_TIMEOUT, $second);
      if(WxPayConfig::CURL_PROXY_HOST != "0.0.0.0"
          &amp;&amp; WxPayConfig::CURL_PROXY_PORT != 0){
          curl_setopt($ch,CURLOPT_PROXY, WxPayConfig::CURL_PROXY_HOST);
          curl_setopt($ch,CURLOPT_PROXYPORT, WxPayConfig::CURL_PROXY_PORT);
      }
      curl_setopt($ch,CURLOPT_URL, $url);
      curl_setopt($ch,CURLOPT_SSL_VERIFYPEER,TRUE);
      curl_setopt($ch,CURLOPT_SSL_VERIFYHOST,2);
  
      curl_setopt($ch, CURLOPT_HEADER, FALSE);
  
      curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
  
      if($useCert == true){
          curl_setopt($ch,CURLOPT_SSLCERTTYPE,'PEM');
          curl_setopt($ch,CURLOPT_SSLCERT, WxPayConfig::SSLCERT_PATH);
          curl_setopt($ch,CURLOPT_SSLKEYTYPE,'PEM');
          curl_setopt($ch,CURLOPT_SSLKEY, WxPayConfig::SSLKEY_PATH);
      }
  
      curl_setopt($ch, CURLOPT_POST, TRUE);
      curl_setopt($ch, CURLOPT_POSTFIELDS, $xml);
  
      $data = curl_exec($ch);
  </code></pre>
  
  <p>I catch the error message of curl_exec and the message as following.</p>
  
  <p>"SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed"</p>