Check if given string is base64 encoded

is_base64.php

private static function isBase64Encoded(string $text): bool
{
    if (false === $decoded = base64_decode($text, true)) {
        return false;
    }
    // check if decoded text consists only of unicode letters, digits and white space
    if (!preg_match('|^[\p{L}\d\s]+$|u', $decoded)) {
        return false;
    }

    return $text === base64_encode($decoded);
}