Is it AD or LDAP to a non-AD directory? There are some additional steps necessary when using a non-AD directory service.
If using AD, you can rely on standard Windows AD logins that handle authentication before a user gets in touch with any QlikView document.
To enable the services to resolve user names (in order to find users and distribute to them), define a Directory Service Connector for Active Directory. Just point the DSC to the/a Domain Controller and enter credentials if needed. That's about it.
And no, the QlikView server doesn't need to be in the same domain as the user or any other machine. QlikView supports users from multiple different domains, and can itself be only present in a single one at a time.