function base64url_encode($plainText) {
    $base64 = base64_encode($plainText);
    $base64url = strtr($base64, '+/=', '-_,');
    return $base64url;
}
 
function base64url_decode($plainText) {
    $base64url = strtr($plainText, '-_,', '+/=');
    $base64 = base64_decode($base64url);
    return $base64;
}