I have a question about windows authentication across multiple domains. DomainA has a user UserA (DomainA\UserA). If DomainB has the same user (DomainB\UserA) and same password, can I connect from DomainB to DomainA using Windows authentication. Or trusted domains is the only way?
Domain identifier is part of login information, which means that DomainB\UserA is not a valid account as far as the server in DomainA goes. You will have to explicitly grant that logon access rights on the SQL box in DomainA. If DomainB is trusted by DomainA, then you can include DomainB\UserA into a group from DomainA and grant that group access rights. This way DomainB\UserA will have access to the server on DomainA.