Nils Gustav Stråbø (2/7/2011)
What security checking does sp_change_users_login do?All it does is map a database user with a login. BOL says nothing about any security checking.
It does some checks on the user that is running the procedure. If it's not a member of the db_owner group it won't let you report or update one, and if the user isn't a member of sysadmin it won't let you auto fix.