Snnipet para convertir una cadena de Base64 a binario

function base64_to_binary($b64str) {
    $letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $b64_table = array_merge(
        str_split($letters),
        str_split(strtolower($letters)),
        range(0, 9),
        ['+', '/']
    );

    $b64_arr_dec = array_map(
        function($e) use ($b64_table) {
            return array_search($e, $b64_table);
        },
        str_split($b64str)
    );

    $b64_arr_bin = array_map('decbin', $b64_arr_dec);
    $b64_arr_bin6 = array_map(
        function($e) {
            return str_pad($e, 6, "0", STR_PAD_LEFT);
        },
        $b64_arr_bin
    );

    $b64_bin6_str = implode('', $b64_arr_bin6);
    $bin_arr = explode(' ', chunk_split($b64_bin6_str, 8, ' '));

    return $bin_arr;
}