if you for some reason need the euid without depending on php-posix being available, try
<?php
function geteuid_without_posix_dependency(): int
{
try {
// this is faster if available
return \posix_geteuid();
} catch (\Throwable $ex) {
// php-posix not available.. fallback to hack
$t = tmpfile();
$ret = fstat($t)["uid"];
fclose($t);
return $ret;
}
}