Return a nonce value - formatted per OpenID spec.
function _openid_nonce() {
// YYYY-MM-DDThh:mm:ssZ, plus some optional extra unique characters.
return gmdate('Y-m-d\\TH:i:s\\Z') . chr(mt_rand(0, 25) + 65) . chr(mt_rand(0, 25) + 65) . chr(mt_rand(0, 25) + 65) . chr(mt_rand(0, 25) + 65);
}