how to encode and decode string in php

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;
}