This page lists the methods for checking who's currently logged in, and for looking up other users by id or login.
Base_AclCommon::i_am_user() - returns true if a user is logged in
Base_AclCommon::i_am_admin() - returns true if the current user is an administrator
Base_AclCommon::i_am_sa() - returns true if the current user is a super administrator
Base_AclCommon::get_user() - returns the current user's id
Base_UserCommon::get_my_user_login() - returns the current user's login
Notice: Base_AclCommon::i_am_user() returns false if the account the user is logged in as doesn't have User rights.
Base_UserCommon::get_user_id($username) - returns the id of the user whose login is $username. Returns false if no such user exists
Base_UserCommon::get_user_login($i) - returns the login of the user whose id is $i. Returns false if no such user exists