PHP example on how to use https://github.com/snowblindroan/mod_admin_rest

mod_admin_rest_example.php

// replace everything that's written in uppercase with your own values
// USERNAME@DOMAIN.TLD needs to be a user who has administrative privileges

function jabber_add_user($username, $password)
{
    $data = json_encode(array('password' => $password));
    curl_setopt_array(
        $ch = curl_init(),
        array(
                CURLOPT_RETURNTRANSFER => true,
                CURLOPT_URL => 'http://localhost:5280/admin_rest/user/'.$username,
                CURLOPT_USERPWD => 'USERNAME@DOMAIN.TLD:PASSWORD',
                CURLOPT_POST => true,
                CURLOPT_POSTFIELDS => $data,
                CURLOPT_HTTPHEADER => array('Host: DOMAIN.TLD', 'Content-Type: application/json', 'Content-Length: '.strlen($data)) 
        )
    );
    curl_exec($ch);
    $code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    curl_close($ch);
    return $code;
}

jabber_add_user('NEW_USER', 'PASSWORD');