* Get the BlockID cookie's value for this block. This is usually the block ID concatenated
* with an HMAC in order to avoid spoofing (T152951), but if wgSecretKey is not set will just
* be the block ID.
* Get the BlockID cookie's value for this block. This is usually the block ID concatenated
* with an HMAC in order to avoid spoofing (T152951), but if wgSecretKey is not set will just
* be the block ID.