Logs in a user and creates a session.
Username or email address.
User password.
User logged in successfully.
Unique ID of the user on the site.
The first name of the user (if any).
The last name of the user (if any).
The display name of the user (if any).
The role type assigned to the user.
The avatar URLs of the user for each avatar size registered.
The email address of the user.
Extra details added via the filter.
A message to developers.