Which My Cloud location you mean? The My Cloud device at your home or the MyCloud.com web portal?
My Cloud username and password for login into the web interface of your My Cloud is stored on the My Cloud device itself.
The account information to login to mycloud.com is stored on the My Cloud servers where the account details for your personal My Cloud access are stored too. But the login credentials to access your My Cloud device at home via Internet aka My Cloud universe is stored again on your local My Cloude device in your home network.
www.MyCloud.com is the portal page to access your My Cloud device at home, the login credentials at mycloud.com are not the same or may not be the same as you use for your device at home.