Standard base64 uses + and / which break in URLs. Swap them for - and _, drop the = padding, and you get a string you can put in path segments and query parameters safely.
PHP
<?php
function base64UrlEncode(string $bytes): string {
return rtrim(strtr(base64_encode($bytes), '+/', '-_'), '=');
}
function base64UrlDecode(string $s): string|false {
$padded = $s . str_repeat('=', (4 - strlen($s) % 4) % 4);
return base64_decode(strtr($padded, '-_', '+/'), true);
}
$payload = base64UrlEncode(random_bytes(32));
echo $payload; // e.g. "X1zR_jc7HpQ..."
$decoded = base64UrlDecode($payload); // bytes round-trip exactlySave your own code snippets
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