If I have a user base that operates on DomainA, and an ASP.NET website that resides/runs on DomainB could I use Windows Authentication as an authn type if they are accessing through the browser? AD on both Domains, and the user base will match each other, but does that even matter if users would be accessing my website application through the browser from another domain? does the caller resolve to the target domain's AD when hitting the page? How does this work?
Different user objects from a different domain are different. The only way a DomainA\User validates to a website on DomainB is if DomainB has an established trust with DomainA. And even in that case, the user will not auto map to the DomainB\User account, it will login with the privileges of DomainA\User.