Did you tick the checkbox marked "Remember account on this computer" when you created your wallet?
If you ticked that checkbox you will be logged in automatically because your browser remembers your pass phrase.
You can delete your pass phrase from your browser in chrome by clicking "settings", then clicking "Show advanced settings", then clicking the "clear browsing data button".
You can delete your pass phrase from your browser in internet explorer by clicking "tools", then "internet options", then the delete button below browsing history.
After that you will be prompted for your pass phrase to login.