Confluence uses Seraph, an open source framework, for HTTP cookie authentication.
Confluence uses two cookies. The first, a JSESSIONID cookie, is created by the Application Server and used for session tracking purposes. The second, the 'Remember my login on this computer' cookie, is generated by Confluence when the user selects the check-box on the log-in page.
The cookie information is always encoded by the server before it is given to a client. A cookie that has been tampered with will be considered to be not valid.
Essentially, the cookie contains a reversible hash of the username and a one-way hash of the user's password. The password is necessary to ensure that the cookie is no longer valid if the user changes their password. The username must be retrievable by the server to identify the user solely from the cookie, which is what the 'Remember my login on this computer' feature does.
At the moment there is no available option for disabling "Remember My Login on this computer" feature via the Admin console. See the workaround here.
The user login Auto Completion functionality is a browser feature, and there is nothing Confluence can enable or disable.
