Windows本地Apache PHP站点连接Cloud SQL Postgres(SSL)故障求助

Windows桌面部署Apache2+PHP网站，原访问本地PostgreSQL，现迁移至Google Cloud SQL Postgres实例，采用公网IP+SSL加密方式。Cloud SQL实例运行正常，所有Windows应用（.Net及.Net Core）均可成功连接，但PHP始终无法建立连接。

已尝试多种连接字符串及参数组合，示例pg_connect字符串（已脱敏）：

host={secret information} port=5432 dbname={secret information} user={secret information} password={secret information} sslmode=require sslcert=client-cert.pem sslkey=client-key.pem

client-cert.pem和client-key.pem为Google生成/下载的证书，在Windows应用中可正常使用，文件存放于c:\apache24\htdocs目录下与HTML/PHP源码同目录，同时也存储了server-ca.pem并尝试引用。

测试页面代码：

<?php  
// Create a custom exception error handler for pg_connect
function exception_error_handler($errno, $errstr, $errfile, $errline ) {
    throw new ErrorException($errstr, $errno, 0, $errfile, $errline);
}
// Set the error handler
set_error_handler("exception_error_handler");

// Force output of all errors
error_reporting(E_ALL);

// Define constants
define('DB_HOST', '{secret information}');
define('DB_USER', '{secret information}');
define('DB_PASS', '{secret information}');
define('DB_NAME', '{secret information}');
define('DB_PORT', '5432');

// Connection string with SSL certificate files
$conn_str  = 'host=' . DB_HOST . ' ';
$conn_str .= 'port=' . DB_PORT . ' ';
$conn_str .= 'dbname=' . DB_NAME . ' ';
$conn_str .= 'user=' . DB_USER . ' ';
$conn_str .= 'password=' . DB_PASS . ' ';
$conn_str .= 'sslmode=require ';
$conn_str .= 'sslcert=client-cert.pem ';
$conn_str .= 'sslkey=client-key.pem ';  

// Try catch block grabbing stored exception
try {
    echo "Attempting pg_connect: " . $conn_str . "<br>";
    $conn=@pg_connect($conn_str);
} catch (Exception $e) {
    echo $e->getMessage();
}

// Attempt Connection
$conn = pg_connect($conn_str) or die('Cannot connect to database.');

// Set SQL String
$sql = 'SELECT * FROM client'; 

// Attempt query and iterate results
if ($result = pg_query($conn, $sql))
{
    while($row=pg_fetch_row($result)) 
    {
        var_dump($row);
    }
}   

// Close it up
pg_close($conn);
?>

测试得到的错误信息：

Attempting pg_connect: host={secret information} port=5432 dbname={secret information} user={secret information} password={secret information} sslmode=require sslcert=client-cert.pem sslkey=client-key.pem
pg_connect(): Unable to connect to PostgreSQL server: FATAL: connection requires a valid client certificate
Fatal error: Uncaught ErrorException: pg_connect(): Unable to connect to PostgreSQL server: FATAL: connection requires a valid client certificate in C:\apache24\htdocs\test.php:38 Stack trace: #0 [internal function]: exception_error_handler(2, 'pg_connect(): U...', 'C:\\apache24\\htd...', 38, Array) #1 C:\apache24\htdocs\test.php(38): pg_connect('host={secret information}...') #2 {main} thrown in C:\apache24\htdocs\test.php on line 38

已尝试添加证书和密钥的完整路径、引入server-ca.pem及添加sslpassword参数，但均无效，恳请提供新的解决思路。

内容的提问来源于stack exchange，提问作者Shane Brodie