From MWCSWiki

Log In:

User: Anonymous User
Preconditions: User is not logged in and has an account
Sunny Day:
1.The user is presented with two fields: User name and Password
2.The user enters their pre-chosen name and enters their password
3.The system displays a logging in message and redirects to the users' main page
Rainy Day:
1.If the user name is invalid, state that no user has registered this name

 1.Kick back to the login screen

2.If the password is invalid, present the user with a password recovery page

 1.The system resets the password to a default password that the user should know

Postconditions: The user is logged into the system under their unique ID. Everything they do and click on is logged and sent into a massive database where “the man” can keep track of them.

Log Out:

User: Registered User
Preconditions: The User is logged in
Sunny Day:
1.The user clicks on the object that allows them to log out (button, link, image)
2.The system logs them out, removing them from the “Active user” list
Rainy Day:
1.The system refuses to log you out, you can't go anywhere.
2.The entire system crashes
3.You log out and forget you had more to do...