I was reading the svn-archive (Section 5.2) to understand how a .onion address is generated.
From my understanding, the "x.y.onion" address, comprises 'x' as 'the authorization cookie', and 'y' as the 'hash of the [onion service] public key'.
I understand that the 'y' part as the onion service is the key for the indexed information on the Tor lookup service, but I don't understand what the 'x' part does.
What is the purpose of the 'x' part--or 'authorization cookie'--in the client's URL bar? Where does it go? What does it do? Why do we need it?
Thank you for taking your time to read this. This is really confusing me.