Sending POST data without form

Simply use: file_get_contents()

// building array of variables
$content = http_build_query(array(
            'username' => 'value',
            'password' => 'value'
            ));
// creating the context change POST to GET if that is relevant 
$context = stream_context_create(array(
            'http' => array(
                'method' => 'POST',
                'content' => $content, )));

$result = file_get_contents('http://www.example.com/page.php', null, $context);
//dumping the reuslt
var_dump($result);

Reference: my answer to a similar question:

function redir(data) {
  document.getElementById('redirect').innerHTML = '<form style="display:none;" position="absolute" method="post" action="location.php"><input id="redirbtn" type="submit" name="value" value=' + data + '></form>';
  document.getElementById('redirbtn').click();
}

<button onclick="redir('dataToBeSent');">Next Page</button>
<div id="redirect"></div>

You can use this method which creates a new hidden form whose "data" is sent by "post" to "location.php" when a button[Next Page] is clicked.

I would highly recommend using curl in such situation, file_fet_content() does work but not at all times, and it could be troublesome to use it in some applications.

Though curl comes in different variations depending on what you want to send and in what method, here is the most common method of posting your data without HTML form using curl.

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, 'http://example.com/request_uri');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POST, 1);
    $post = array(
        'data1' => 'value1',
        'data2' => $value2
    );
    curl_setopt($ch, CURLOPT_POSTFIELDS, $post);

    $result = curl_exec($ch);
    if (curl_errno($ch)) {
        echo 'Error:' . curl_error($ch);
    }
    curl_close($ch);
    
    //do what you want with the responce
    var_dump($result)