PHP：修剪superglobals中所有值的副作用（$ _GET，$ _POST，$ _COOKIE，$ _REQUEST）

I know that many people believe it is wrong to edit Superglobals in PHP. But I found myself to always trim user input in every controller of my webapp. To solve the problem once and for all I now just trim all values of these Superglobals like that:

# trim ALL inputs
foreach ($_REQUEST as $key => $value) {
    $_REQUEST[$key] = trim($value);
}
foreach ($_COOKIE as $key => $value) {
    $_COOKIE[$key] = trim($value);
}
foreach ($_GET as $key => $value) {
    $_GET[$key] = trim($value);
}
foreach ($_POST as $key => $value) {
    $_POST[$key] = trim($value);
}

Some users might want to define a password that starts or ends with a whitespace. Apart from that I cannot think of any usecase where trimming might do any harm.

Has anybody else tried to trim these Superglobals and ran into strange side effects that I should be aware of?