function registerLoginHandler() {
    var form = document.getElementById('loginform');
    
    form.onsubmit = checkCredentials;
}

function checkCredentials() {
    var username, password, challenge, response;
    var form = document.getElementById('loginform');
    
    // Access username, login, profileName, userid ... etc. by numerical index
    username = form.username.value;
    password = form.password.value;

    if (password != "") {
        challenge = form.challenge.value;
        response = hex_md5(username + hex_md5(password) + challenge);
        form.password.value = '';
        form.response.value = response;
    } else {
        return false;
    }
    
    return true;
}

window.onload = registerLoginHandler;