<?php
    $username =  "abc"; //$_POST['user'];
    $password = "abc"; //$_POST['pass'];

    if (isset($username, $password)) {
        $params = array('grant_type' => 'password', 'username' => $username, 'password' => $password);
        $query = http_build_query($params);

        $contextData = array(
            'method' => 'POST',
            'header' => "Content-Type: application/x-www-form-urlencoded\r\n",
            'content' => $query
        );

        $context = stream_context_create(array('http' => $contextData));

        $result = file_get_contents(
            "https://mitglieder.leo-clubs.de/LeoAPI/api/memberlogin",  // page url
            false,
            $context);

        echo 'requested';
        var_dump($result);
    }
?>