具有SSL证书的cURL失败:错误58无法设置私钥文件

我正在尝试使用cURL连接到远程主机.连接需要使用证书和受密码保护的私钥.到目前为止，我无法使用以下代码:

I'm trying to connect to a remote host using cURL. The connection requires the use of a certificate and a private key which is password protected. So far I'm unsuccessful with this code below:

<?php
    $wsdl       = 'https://domain.com/?wsdl';
    $certFile   = getcwd() . '/auth/cert.pem';
    $keyFile    = getcwd() . '/auth/key.pem';
    $password   = 'pwd';

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL,           $wsdl);
    curl_setopt($ch, CURLOPT_SSLCERT,       $certFile);
    curl_setopt($ch, CURLOPT_SSLKEYPASSWD,  $password);
    curl_setopt($ch, CURLOPT_SSLKEY,        $keyFile);
    #curl_setopt($ch, CURLOPT_FRESH_CONNECT, true);
    #curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    #curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
    $output = curl_exec($ch);

    var_dump(curl_errno($ch));
    var_dump(curl_error($ch));

我一直得到的结果是错误58:unable to set private key file: '/home/.../domains/.../public_html/auth/key.pem' type PEM.

The result I keep getting is error 58: unable to set private key file: '/home/.../domains/.../public_html/auth/key.pem' type PEM.

到目前为止我已经尝试过的事情:

Things I've tried so far:

• 按照以下建议检查密钥文件是否可读:无法使用libcurl访问需要客户端身份验证的网站.到目前为止没有运气.
• 玩弄了其他一些选项，例如SLL_VERIFY_PEER，SSL_VERIFY_HOST，SSL_CERTTYPE和其他对于官方PHP文档而言似乎微不足道的选项.到目前为止没有运气.

• Check if the key-file is readable as suggested here: Unable to use libcurl to access a site requiring client authentication. Trying to pass the file through openssl_private_key() gives me a resource, and not a boolean. So this seems good.
• Switch the order of the content in the key.pem file as suggested here: Unable to use libcurl to access a site requiring client authentication. No luck so far.
• Played around with some other options like SLL_VERIFY_PEER, SSL_VERIFY_HOST, SSL_CERTTYPE and other options which seemed trivial regarding the official PHP-docs. No luck so far.

我很确定问题出在我的配置中，但是我不确定在哪里看.

I'm pretty sure the problem lies somehwere in my configuration, but I'm not sure where to look.