PHP の「file_get_contents()」を使用してデータを投稿するにはどうすればよいですか?

// Build the POST data as a query string
$postdata = http_build_query([
    'var1' => 'some content',
    'var2' => 'doh'
]);

// Create a stream context with HTTP options
$opts = [
    'http' => [
        'method' => 'POST',
        'header' => 'Content-Type: application/x-www-form-urlencoded',
        'content' => $postdata
    ]
];

// Create the stream context
$context = stream_context_create($opts);

// Send the HTTP POST request and retrieve the response
$result = file_get_contents('http://example.com/submit.php', false, $context);