Hi,
When using a CDN that supports it, you can set a token generation in the admin console->publishers->your partner->profiles->delivery profiles.
Once you select a delivery type, you will have a form which includes:
"Tokenizer Configuration"
where you can select a token type, input a key and select the window size.
That would mean all delivery URLs will include this token and, once expired, the CDN will refuse to serve the content until a new token is generated.
This is mostly useful to prevent people from getting the direct URL for the entry using an HTTP sniffer and hitting it from outside the player later on.